patch 8.2.4968: reading past end of the line when C-indenting

Problem:    Reading past end of the line when C-indenting.
Solution:   Check for NUL.

src/cindent.c

@@ -89,7 +89,7 @@ skip_string(char_u *p)
 		while (vim_isdigit(p[i - 1]))   // '\000'
 		    ++i;
 	    }
-	    if (p[i] == '\'')		    // check for trailing '
+	    if (p[i - 1] != NUL && p[i] == '\'')    // check for trailing '
 	    {
 		p += i;
 		continue;