patch 8.2.2357: Vim9: crash when parsing function return type fails

Problem:    Vim9: crash when parsing function return type fails.
Solution:   Bail out and set return type to "unknown". (closes #7685)

src/testdir/test_vim9_func.vim

@@ -197,6 +197,17 @@ def Test_return_nothing()
   s:nothing->assert_equal(1)
 enddef
 
+def Test_return_invalid()
+  var lines =<< trim END
+    vim9script
+    def Func(): invalid
+      return xxx
+    enddef
+    defcompile
+  END
+  CheckScriptFailure(lines, 'E1010:', 2)
+enddef
+
 func Increment()
   let g:counter += 1
 endfunc

src/userfunc.c

@@ -3886,6 +3886,12 @@ define_function(exarg_T *eap, char_u *name_arg)
 	{
 	    p = ret_type;
 	    fp->uf_ret_type = parse_type(&p, &fp->uf_type_list, TRUE);
+	    if (fp->uf_ret_type == NULL)
+	    {
+		fp->uf_ret_type = &t_void;
+		SOURCING_LNUM = lnum_save;
+		goto erret;
+	    }
 	}
 	SOURCING_LNUM = lnum_save;
     }

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2357,
 /**/
     2356,
 /**/