patch 8.0.1254: undefined left shift in gethexchrs()

Problem:    Undefined left shift in gethexchrs(). (geeknik)
Solution:   Use unsigned long. (idea by Christian Brabandt, closes #2255)
diff --git a/src/regexp_nfa.c b/src/regexp_nfa.c
index 86061a3..feb17bc 100644
--- a/src/regexp_nfa.c
+++ b/src/regexp_nfa.c
@@ -1522,7 +1522,7 @@
 		case 'u':   /* %uabcd hex 4 */
 		case 'U':   /* %U1234abcd hex 8 */
 		    {
-			int nr;
+			long nr;
 
 			switch (c)
 			{
@@ -2040,7 +2040,7 @@
     int		greedy = TRUE;      /* Braces are prefixed with '-' ? */
     parse_state_T old_state;
     parse_state_T new_state;
-    int		c2;
+    long	c2;
     int		old_post_pos;
     int		my_post_start;
     int		quest;