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;

src/testdir/test_cindent.vim

@@ -5319,6 +5319,13 @@ func Test_cindent_change_multline()
   close!
 endfunc
 
+" This was reading past the end of the line
+func Test_cindent_check_funcdecl()
+  new
+  sil norm o0('\0=L
+  bwipe!
+endfunc
+
 func Test_cindent_scopedecls()
   new
   setl cindent ts=4 sw=4

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4968,
 /**/
     4967,
 /**/