patch 8.2.4925: trailing backslash may cause reading past end of line

Problem:    Trailing backslash may cause reading past end of line.
Solution:   Check for NUL after backslash.
diff --git a/src/textobject.c b/src/textobject.c
index e4a7db3..edaa64c 100644
--- a/src/textobject.c
+++ b/src/textobject.c
@@ -1664,7 +1664,11 @@
 	if (c == NUL)
 	    return -1;
 	else if (escape != NULL && vim_strchr(escape, c))
+	{
 	    ++col;
+	    if (line[col] == NUL)
+		return -1;
+	}
 	else if (c == quotechar)
 	    break;
 	if (has_mbyte)