patch 8.2.2890: text property duplicated when data block splits

Problem:    Text property duplicated when data block splits.
Solution:   Do not continue text prop from previous line. (closes #8261)

src/structs.h

@@ -774,6 +774,7 @@ typedef struct memline
 #define ML_APPEND_NEW	    1	// starting to edit a new file
 #define ML_APPEND_MARK	    2	// mark the new line
 #define ML_APPEND_UNDO	    4	// called from undo
+#define ML_APPEND_NOPROP    8	// do not continue textprop from previous line
 
 
 /*