patch 8.2.4878: valgrind warning for using uninitialized variable

Problem:    Valgrind warning for using uninitialized variable.
Solution:   Initialize the type of newtv.

src/strings.c

@@ -898,6 +898,7 @@ string_filter_map(
 	    break;
 	len = (int)STRLEN(tv.vval.v_string);
 
+	newtv.v_type = VAR_UNKNOWN;
 	set_vim_var_nr(VV_KEY, idx);
 	if (filter_map_one(&tv, expr, filtermap, &newtv, &rem) == FAIL
 		|| did_emsg)

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4878,
 /**/
     4877,
 /**/