Use ImagingNewDirty() in RankFilter and remove ImagingFill() in font.getmask() (#9744)

Co-authored-by: Andrew Murray <radarhere@users.noreply.github.com>

Author: akx

src/_imaging.c

@@ -2882,9 +2882,6 @@ _font_getmask(ImagingFontObject *self, PyObject *args) {
         return ImagingError_MemoryError();
     }
 
-    b = 0;
-    (void)ImagingFill(im, &b);
-
     b = self->baseline;
     for (x = 0; text[i]; i++) {
         glyph = &self->glyphs[text[i]];

src/libImaging/RankFilter.c

@@ -84,7 +84,8 @@ MakeRankFunction(UINT8) MakeRankFunction(INT32) MakeRankFunction(FLOAT32)
         return (Imaging)ImagingError_ValueError("bad rank value");
     }
 
-    imOut = ImagingNew(im->mode, im->xsize - 2 * margin, im->ysize - 2 * margin);
+    // Every output pixel is written by the rank loop below
+    imOut = ImagingNewDirty(im->mode, im->xsize - 2 * margin, im->ysize - 2 * margin);
     if (!imOut) {
         return NULL;
     }