vcl: document parameter of loadImage

Change-Id: Icbd617c3ce1571a867e0ebe749d40125275631a6

include/vcl/imagerepository.hxx

@@ -44,6 +44,9 @@ namespace vcl
                 will take the image upon successful return.
             @param  bSearchLanguageDependent
                 determines whether a language-dependent image is to be searched.
+            @param  loadMissing
+                if set to true, then load a default image if no image can be found,
+                otherwise don't load anything
             @return
                 whether or not the image could be loaded successfully.
         */