patch 8.0.0623: error for invalid regexp is not very informative

Problem:    The message "Invalid range" is used for multiple errors.
Solution:   Add two more specific error messages. (Itchyny, Ken Hamada)
diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index c490acb..4e111f1 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -1853,7 +1853,7 @@
 			endc = startc;
 			startc = oldstartc;
 			if (startc > endc)
-			    EMSG_RET_FAIL(_(e_invrange));
+			    EMSG_RET_FAIL(_(e_reverse_range));
 
 			if (endc > startc + 2)
 			{