patch 8.0.1225: no check for spell region being zero

Problem:    No check for spell region being zero. (geeknik)
Solution:   Check for zero. (closes #2252)
diff --git a/src/spellfile.c b/src/spellfile.c
index 6188aaf..f6d7a64 100644
--- a/src/spellfile.c
+++ b/src/spellfile.c
@@ -4277,7 +4277,7 @@
 		    flags |= WF_REGION;
 
 		    l = *p - '0';
-		    if (l > spin->si_region_count)
+		    if (l == 0 || l > spin->si_region_count)
 		    {
 			smsg((char_u *)_("Invalid region nr in %s line %d: %s"),
 							  fname, lnum, p);