patch 9.0.1251: checking returned value of ga_grow() is inconsistent

Problem:    Checking returned value of ga_grow() is inconsistent.
Solution:   Check for FAIL instaed of "not OK". (Yegappan Lakshmanan,
            closes #11897)
diff --git a/src/map.c b/src/map.c
index 244636f..9be67cd 100644
--- a/src/map.c
+++ b/src/map.c
@@ -2983,7 +2983,7 @@
 	    b = i;
     }
 
-    if (ga_grow(&langmap_mapga, 1) != OK)
+    if (ga_grow(&langmap_mapga, 1) == FAIL)
 	return;  // out of memory
 
     // insert new entry at position "a"