patch 8.2.3062: internal error when adding several text properties

Problem:    Internal error when adding several text properties.
Solution:   Do not handle text properties when deleting a line for splitting a
            data block. (closes #8466)

src/structs.h

@@ -769,6 +769,7 @@ typedef struct memline
 // Values for the flags argument of ml_delete_flags().
 #define ML_DEL_MESSAGE	    1	// may give a "No lines in buffer" message
 #define ML_DEL_UNDO	    2	// called from undo, do not update textprops
+#define ML_DEL_NOPROP	    4	// splitting data block, do not update textprops
 
 // Values for the flags argument of ml_append_int().
 #define ML_APPEND_NEW	    1	// starting to edit a new file