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/os_win32.c b/src/os_win32.c
index e80533b..884ef0d 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -5725,7 +5725,7 @@
 		    size_t	lkey = wcslen(wkey);
 		    size_t	lval = wcslen(wval);
 
-		    if (ga_grow(gap, (int)(lkey + lval + 2)) != OK)
+		    if (ga_grow(gap, (int)(lkey + lval + 2)) == FAIL)
 			continue;
 		    for (n = 0; n < lkey; n++)
 			*((WCHAR*)gap->ga_data + gap->ga_len++) = wkey[n];