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.
diff --git a/src/testdir/test_cindent.vim b/src/testdir/test_cindent.vim
index dbd4aa0..c65a0da 100644
--- a/src/testdir/test_cindent.vim
+++ b/src/testdir/test_cindent.vim
@@ -5319,6 +5319,13 @@
   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