patch 8.1.0654: when deleting a line text property flags are not adjusted

Problem:    When deleting a line text property flags are not adjusted.
Solution:   Adjust text property flags in preceding and following lines.

src/misc2.c

@@ -1350,6 +1350,20 @@ vim_strnsave(char_u *string, int len)
     return p;
 }
 
+/*
+ * Copy "p[len]" into allocated memory, ignoring NUL characters.
+ * Returns NULL when out of memory.
+ */
+    char_u *
+vim_memsave(char_u *p, int len)
+{
+    char_u *ret = alloc((unsigned)len);
+
+    if (ret != NULL)
+	mch_memmove(ret, p, (size_t)len);
+    return ret;
+}
+
 /*
  * Same as vim_strsave(), but any characters found in esc_chars are preceded
  * by a backslash.