urlmon: Better error handling in file protocol.

dlls/urlmon/file.c

@@ -119,6 +119,9 @@ static HRESULT WINAPI FileProtocol_Start(IInternetProtocol *iface, LPCWSTR szUrl
 
     ReleaseBindInfo(&bindinfo);
 
+    if(!szUrl || !*szUrl)
+        return E_INVALIDARG;
+
     if(lstrlenW(szUrl) < sizeof(wszFile)/sizeof(WCHAR)
             || memcmp(szUrl, wszFile, sizeof(wszFile)))
         return MK_E_SYNTAX;

dlls/urlmon/tests/protocol.c

@@ -1384,6 +1384,16 @@ static void test_file_protocol_fail(void)
     CHECK_CALLED(ReportProgress_SENDINGREQUEST);
     CHECK_CALLED(ReportResult);
 
+    SET_EXPECT(GetBindInfo);
+    hres = IInternetProtocol_Start(protocol, NULL, &protocol_sink, &bind_info, 0, 0);
+    ok(hres == E_INVALIDARG, "Start failed: %08x, expected E_INVALIDARG\n", hres);
+    CHECK_CALLED(GetBindInfo);
+
+    SET_EXPECT(GetBindInfo);
+    hres = IInternetProtocol_Start(protocol, emptyW, &protocol_sink, &bind_info, 0, 0);
+    ok(hres == E_INVALIDARG, "Start failed: %08x, expected E_INVALIDARG\n", hres);
+    CHECK_CALLED(GetBindInfo);
+
     IInternetProtocol_Release(protocol);
 }