patch 8.2.2341: expresison command line completion incomplete after "g:"

Problem:    Expresison command line completion shows variables but not
            functions after "g:". (Gary Johnson)
Solution:   Prefix "g:" when needed to a global function.

src/evalvars.c

@@ -1952,7 +1952,7 @@ static int	varnamebuflen = 0;
 /*
  * Function to concatenate a prefix and a variable name.
  */
-    static char_u *
+    char_u *
 cat_prefix_varname(int prefix, char_u *name)
 {
     int		len;