Fix invalid boolean type conversions

[Kimapr]

on my GNU Guix System computer (where i can't use the pre-built binaries because they rely on dynamic linking which needs special considerations in GNU Guix System similar to ones in NixOS) when trying to build node-canvas i get this error:

make: Entering directory '/home/kimapr/stuff/software/node-canvas/build'
  SOLINK_MODULE(target) Release/obj.target/canvas-postbuild.node
  COPY Release/canvas-postbuild.node
  CXX(target) Release/obj.target/canvas/src/bmp/BMPParser.o
  CXX(target) Release/obj.target/canvas/src/Canvas.o
In file included from ../src/Canvas.cc:27:
../src/JPEGStream.h: In function ‘boolean empty_closure_output_buffer(j_compress_ptr)’:
../src/JPEGStream.h:39:10: error: cannot convert ‘bool’ to ‘boolean’ in return
   39 |   return true;
      |          ^~~~
../src/JPEGStream.h: In function ‘void encode_jpeg(jpeg_compress_struct, cairo_surface_t*, int, bool, int, int)’:
../src/JPEGStream.h:96:52: error: invalid conversion from ‘int’ to ‘boolean’ [-fpermissive]
   96 |   jpeg_set_quality(&cinfo, quality, (quality < 25) ? 0 : 1);
      |                                     ~~~~~~~~~~~~~~~^~~~~~~
      |                                                    |
      |                                                    int
In file included from ../src/closure.h:13,
                 from ../src/Canvas.h:8,
                 from ../src/Canvas.cc:3:
/gnu/store/vwq4dsfk2j8a94b1c7qmg2p0vs631xxk-libjpeg-9f/include/jpeglib.h:993:44: note:   initializing argument 3 of ‘void jpeg_set_quality(j_compress_ptr, int, boolean)’
  993 |                                    boolean force_baseline));
      |                                    ~~~~~~~~^~~~~~~~~~~~~~
/gnu/store/vwq4dsfk2j8a94b1c7qmg2p0vs631xxk-libjpeg-9f/include/jpeglib.h:877:25: note: in definition of macro ‘JPP’
  877 | #define JPP(arglist)    arglist
      |                         ^~~~~~~
In file included from /gnu/store/b1dkq30pbiwwz5ykann1k5n39mavf069-glib-2.86.0/lib/glib-2.0/include/glibconfig.h:9,
                 from /gnu/store/b1dkq30pbiwwz5ykann1k5n39mavf069-glib-2.86.0/include/glib-2.0/glib/gtypes.h:34,
                 from /gnu/store/b1dkq30pbiwwz5ykann1k5n39mavf069-glib-2.86.0/include/glib-2.0/glib/galloca.h:34,
                 from /gnu/store/b1dkq30pbiwwz5ykann1k5n39mavf069-glib-2.86.0/include/glib-2.0/glib.h:32,
                 from /gnu/store/b1dkq30pbiwwz5ykann1k5n39mavf069-glib-2.86.0/include/glib-2.0/gobject/gbinding.h:30,
                 from /gnu/store/b1dkq30pbiwwz5ykann1k5n39mavf069-glib-2.86.0/include/glib-2.0/glib-object.h:24,
                 from /gnu/store/bs30dsx41yk626d25vrz4b0qixmmfsbd-pango-1.56.4/include/pango-1.0/pango/pango-coverage.h:25,
                 from /gnu/store/bs30dsx41yk626d25vrz4b0qixmmfsbd-pango-1.56.4/include/pango-1.0/pango/pango-font.h:25,
                 from /gnu/store/bs30dsx41yk626d25vrz4b0qixmmfsbd-pango-1.56.4/include/pango-1.0/pango/pango-attributes.h:25,
                 from /gnu/store/bs30dsx41yk626d25vrz4b0qixmmfsbd-pango-1.56.4/include/pango-1.0/pango/pango.h:25,
                 from /gnu/store/bs30dsx41yk626d25vrz4b0qixmmfsbd-pango-1.56.4/include/pango-1.0/pango/pangocairo.h:25,
                 from ../src/Canvas.h:12:
/gnu/store/b1dkq30pbiwwz5ykann1k5n39mavf069-glib-2.86.0/include/glib-2.0/glib/gmacros.h:935:18: error: cannot convert ‘bool’ to ‘boolean’
  935 | #define TRUE    (!FALSE)
      |                 ~^~~~~~~
      |                  |
      |                  bool
../src/JPEGStream.h:101:31: note: in expansion of macro ‘TRUE’
  101 |   jpeg_start_compress(&cinfo, TRUE);
      |                               ^~~~
/gnu/store/vwq4dsfk2j8a94b1c7qmg2p0vs631xxk-libjpeg-9f/include/jpeglib.h:1014:47: note:   initializing argument 2 of ‘void jpeg_start_compress(j_compress_ptr, boolean)’
 1014 |                                       boolean write_all_tables));
      |                                       ~~~~~~~~^~~~~~~~~~~~~~~~
/gnu/store/vwq4dsfk2j8a94b1c7qmg2p0vs631xxk-libjpeg-9f/include/jpeglib.h:877:25: note: in definition of macro ‘JPP’
  877 | #define JPP(arglist)    arglist
      |                         ^~~~~~~
make: *** [canvas.target.mk:189: Release/obj.target/canvas/src/Canvas.o] Error 1
make: Leaving directory '/home/kimapr/stuff/software/node-canvas/build'

I have no idea what is boolean type and why it exists when we've already had bool built into C++ itself since eons ago and I have even less idea why one can't be implicitly converted into the other or from an int but it is what it is.

Just adding some casts fixes the compile error. It's probably better to fix the actual boolean type so that it allows implicit conversions but I don't even know where it is defined so i'm not doing that