Fixed bugs #471 and #480

--HG--
branch : SDL-1.2

src/video/quartz/SDL_QuartzEvents.m

@@ -270,6 +270,8 @@ static void QZ_DoKey (_THIS, int state, NSEvent *event) {
         [field_edit interpretKeyEvents:[NSArray arrayWithObject:event]];
         chars = [ event characters ];
         numChars = [ chars length ];
+        if (numChars > 0)
+            [field_edit setString:@""];
     } else {
         numChars = 0;
     }