patch 9.0.0665: setting 'cmdheight' has no effect if last window was resized

Problem:    Setting 'cmdheight' has no effect if last window was resized.
Solution:   Do apply 'cmdheight' when told to.  Use the frame height instead
            of the cmdline_row.  (closes #11286)
diff --git a/src/window.c b/src/window.c
index 52c458e..79ff5a4 100644
--- a/src/window.c
+++ b/src/window.c
@@ -6644,7 +6644,7 @@
 }
 
 /*
- * command_height: called whenever p_ch has been changed
+ * Command_height: called whenever p_ch has been changed.
  */
     void
 command_height(void)
@@ -6663,6 +6663,9 @@
     if (p_ch > old_p_ch && cmdline_row <= Rows - p_ch)
 	return;
 
+    // Update cmdline_row to what it should be: just below the last window.
+    cmdline_row = topframe->fr_height;
+
     // If cmdline_row is smaller than what it is supposed to be for 'cmdheight'
     // then set old_p_ch to what it would be, so that the windows get resized
     // properly for the new value.