Add missing ui files to meson.build

ui/filebutton.py and ui/pathlabel.py were missing from meld.ui
causing meld to fail to launch.

Author: mydongistiny

meld/meson.build

@@ -49,6 +49,7 @@ folders = {
     'ui/bufferselectors.py',
     'ui/cellrenderers.py',
     'ui/emblemcellrenderer.py',
+    'ui/filebutton.py',
     'ui/findbar.py',
     'ui/gladesupport.py',
     'ui/gtkcompat.py',
@@ -57,6 +58,7 @@ folders = {
     'ui/msgarea.py',
     'ui/notebook.py',
     'ui/notebooklabel.py',
+    'ui/pathlabel.py',
     'ui/recentselector.py',
     'ui/statusbar.py',
     'ui/util.py',