Avoid 0x0 window when autosaved dimension missing

This fixes a bug where the first window would be tiny if no autosaved
dimensions existed on startup.

src/MacVim/gui_macvim.m

@@ -133,6 +133,11 @@ gui_macvim_after_fork_init()
             && (rows > 4 && rows < 1000 && cols > 29 && cols < 4000)) {
         gui.num_rows = rows;
         gui.num_cols = cols;
+    } else {
+        // Use the defaults (typically 80x24), if there are no autosaved rows &
+        // columns.
+        gui.num_rows = Rows;
+        gui.num_cols = Columns;
     }
 
     // Check which code path to take for string drawing.

src/ui.c

@@ -310,7 +310,9 @@ ui_get_shellsize()
 #ifdef FEAT_GUI
     if (gui.in_use
 # ifdef FEAT_GUI_MACVIM
-            || gui.starting     /* TODO: Do this check for all GUIs? */
+            /* Avoid using terminal dimensions for GUI window.  MacVim
+             * autosaves the dimensions of the first window. */
+            || gui.starting
 # endif
             )
 	retval = gui_get_shellsize();