patch 9.0.0552: crash when using NUL in buffer that uses :source

Problem:    Crash when using NUL in buffer that uses :source.
Solution:   Don't get a next line when skipping over NL.

src/eval.c

@@ -253,7 +253,7 @@ eval_expr_typval(typval_T *expr, typval_T *argv, int argc, typval_T *rettv)
 	    if (fc == NULL)
 		return FAIL;
 
-	    // Shortcut to call a compiled function without overhead.
+	    // Shortcut to call a compiled function with minimal overhead.
 	    r = call_def_function(partial->pt_func, argc, argv,
 					  DEF_USE_PT_ARGV, partial, fc, rettv);
 	    remove_funccal();
@@ -2291,7 +2291,7 @@ eval_next_non_blank(char_u *arg, evalarg_T *evalarg, int *getnext)
 
 	if (next != NULL)
 	{
-	    *getnext = TRUE;
+	    *getnext = *p != NL;
 	    return skipwhite(next);
 	}
     }

src/testdir/test_source.vim

@@ -665,5 +665,22 @@ func Test_source_buffer_long_line()
   call delete('Xtest.vim')
 endfunc
 
+func Test_source_buffer_with_NUL_char()
+  " This was trying to use a line below the buffer.
+  let lines =<< trim END
+      if !exists('g:loaded')
+        let g:loaded = 1
+        source
+      endif
+  END
+  " Can't have a NL in heredoc
+  let lines += ["silent! vim9 echo [0 \<NL> ? 'a' : 'b']"]
+  call writefile(lines, 'XsourceNul', '')
+  edit XsourceNul
+  source
+
+  bwipe!
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    552,
 /**/
     551,
 /**/