FileChooser (Linux): Better sanitize file extension patterns for Zenity

With Zenity 4.2.2, I was seeing that file extension patterns with a
trailing space (example below) were causing the file chooser process to
start, but the window never became visible.

zenity --file-selection --file-filter="*.a *.b "

Author: reuk

modules/juce_gui_basics/native/juce_FileChooser_linux.cpp

@@ -208,7 +208,7 @@ class FileChooser::Native final : public FileChooser::Pimpl,
         }
 
         args.add (startPath.getFullPathName());
-        args.add ("(" + owner.filters.replaceCharacter (';', ' ') + ")");
+        args.add ("(" + owner.filters.replaceCharacter (';', ' ').trim() + ")");
     }
 
     void addZenityArgs()
@@ -266,6 +266,7 @@ class FileChooser::Native final : public FileChooser::Pimpl,
         {
             StringArray tokens;
             tokens.addTokens (owner.filters, ";,|", "\"");
+            tokens.removeEmptyStrings();
 
             args.add ("--file-filter=" + tokens.joinIntoString (" "));
         }