Fix underlining spaces.

Author: s4y

src/MacVim/MMCoreTextView.m

@@ -1431,15 +1431,14 @@ - (void)setString:(NSString *)string
         GridCellInsertionPoint insertionPoint = {0};
         if (flags & DRAW_TRANSP)
             insertionPoint = cell->insertionPoint;
-        if ([substring isEqualToString:@" "]) {
-            *cell = (GridCell){ .bg = bg, .insertionPoint = insertionPoint };
-            return;
-        }
-    
-        NSString *characterString = [characterStrings member:substring];
-        if (!characterString) {
-            characterString = substring;
-            [characterStrings addObject:characterString];
+
+        NSString *characterString = nil;
+        if (![substring isEqualToString:@" "]) {
+            characterString = [characterStrings member:substring];
+            if (!characterString) {
+                characterString = substring;
+                [characterStrings addObject:characterString];
+            }
         }
         *cell = (GridCell){
             .bg = bg,