patch 9.1.0798: too many strlen() calls in cmdhist.c

Problem:  too many strlen() calls in cmdhist.c
Solution: refactor code and remove strlen() calls
          (John Marriott)

closes: #15888

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/ex_cmds.c

@@ -5192,10 +5192,10 @@ ex_global(exarg_T *eap)
 	delim = *cmd;		// get the delimiter
 	++cmd;			// skip delimiter if there is one
 	pat = cmd;		// remember start of pattern
-	patlen = STRLEN(pat);
 	cmd = skip_regexp_ex(cmd, delim, magic_isset(), &eap->arg, NULL, NULL);
 	if (cmd[0] == delim)		    // end delimiter found
 	    *cmd++ = NUL;		    // replace it with a NUL
+	patlen = STRLEN(pat);
     }
 
     if (search_regcomp(pat, patlen, &used_pat, RE_BOTH, which_pat, SEARCH_HIS,