patch 8.2.0449: Vim9: crash if return type is invalid

Problem:    Vim9: crash if return type is invalid. (Yegappan Lakshmanan)
Solution:   Always return some type, not NULL.

src/testdir/test_vim9_script.vim

@@ -269,6 +269,9 @@ def Test_return_type_wrong()
   CheckScriptFailure(['def Func(): string', 'return 1', 'enddef'], 'expected string but got number')
   CheckScriptFailure(['def Func(): void', 'return "a"', 'enddef'], 'expected void but got string')
   CheckScriptFailure(['def Func()', 'return "a"', 'enddef'], 'expected void but got string')
+
+  CheckScriptFailure(['def Func(): list', 'return []', 'enddef'], 'E1008:')
+  CheckScriptFailure(['def Func(): dict', 'return {}', 'enddef'], 'E1008:')
 enddef
 
 def Test_arg_type_wrong()

src/version.c

@@ -738,6 +738,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    449,
 /**/
     448,
 /**/

src/vim9compile.c

@@ -1375,19 +1375,19 @@ parse_type_member(char_u **arg, type_T *type, garray_T *type_list)
 	    emsg(_("E1007: No white space allowed before <"));
 	else
 	    emsg(_("E1008: Missing <type>"));
-	return NULL;
+	return type;
     }
     *arg = skipwhite(*arg + 1);
 
     member_type = parse_type(arg, type_list);
     if (member_type == NULL)
-	return NULL;
+	return type;
 
     *arg = skipwhite(*arg);
     if (**arg != '>')
     {
 	emsg(_("E1009: Missing > after type"));
-	return NULL;
+	return type;
     }
     ++*arg;