added some braces to silence gcc warnings

src/glut/glx/layerutil.c

@@ -129,26 +129,29 @@ __glutXGetLayerVisualInfo(Display * dpy, long lvinfo_mask,
           break;
         }
     }
-    if (lvinfo_mask & VisualLayerMask)
+    if (lvinfo_mask & VisualLayerMask) {
       if (overlayInfo == NULL) {
         if (lvinfo_template->layer != 0)
           continue;
       } else if (lvinfo_template->layer != overlayInfo->layer)
         continue;
-    if (lvinfo_mask & VisualTransparentType)
+    }
+    if (lvinfo_mask & VisualTransparentType) {
       if (overlayInfo == NULL) {
         if (lvinfo_template->type != None)
           continue;
       } else if (lvinfo_template->type !=
         overlayInfo->transparent_type)
         continue;
-    if (lvinfo_mask & VisualTransparentValue)
+    }
+    if (lvinfo_mask & VisualTransparentValue) {
       if (overlayInfo == NULL)
         /* Non-overlay visuals have no sense of
            TransparentValue. */
         continue;
       else if (lvinfo_template->value != overlayInfo->value)
         continue;
+    }
     layerInfo[count].vinfo = *pVinfo;
     if (overlayInfo == NULL) {
       layerInfo[count].layer = 0;