patch 8.1.0638: text property highlighting is off by one column

Problem:    Text property highlighting is off by one column. (Bjorn Linse)
Solution:   Update text property highlighting earlier.  Let it overrule syntax
            highlighting.
diff --git a/src/structs.h b/src/structs.h
index 2f2795a..aa59bff 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -705,7 +705,7 @@
  */
 typedef struct textprop_S
 {
-    colnr_T	tp_col;		// start column
+    colnr_T	tp_col;		// start column (one based)
     colnr_T	tp_len;		// length in bytes
     int		tp_id;		// identifier
     int		tp_type;	// property type