Fix typo

Change-Id: Ie2e3cfa3c35f5ccb59420afb13f5142ecdcb659e
Reviewed-on: https://gerrit.libreoffice.org/7033Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

svx/source/sidebar/paragraph/ParaPropertyPanel.src

@@ -49,11 +49,11 @@
 
 Image IMG_BACK_COLOR
 {
-    ImageBitmap = Bitmap{File = "symphony/sc_backgroundcolor.bmp";};
+    ImageBitmap = Bitmap{File = "symphony/sc_backgroundcolor.png";};
 };
 Image IMG_BACK_COLOR_H
 {
-    ImageBitmap = Bitmap{File = "symphony/sch_backgroundcolor.bmp";};
+    ImageBitmap = Bitmap{File = "symphony/sch_backgroundcolor.png";};
 };
 Image IMG_SPACE3
 {