Fix excessive error login for FLIPPER_BROWSER_PORT

Summary: Prior to this diff, an empty env var FLIPPER_BROWSER_PORT resulted in an error

Reviewed By: passy

Differential Revision: D33712720

fbshipit-source-id: 760fc92bbf44268ec428a3d2947735d5cf8567b7

desktop/flipper-server-core/src/FlipperServerConfig.tsx

@@ -63,16 +63,19 @@ export function getServerPortsConfig(): {
     }
   }
 
-  const portBrowserOverride = parseEnvironmentVariableAsNumber(
+  let portBrowserOverride: number | undefined;
+  if (process.env.FLIPPER_BROWSER_PORT) {
+    portBrowserOverride = parseEnvironmentVariableAsNumber(
       'FLIPPER_BROWSER_PORT',
     );
-  if (portBrowserOverride === undefined) {
+    if (!portBrowserOverride) {
       console.error(
         `Ignoring malformed FLIPPER_BROWSER_PORT env variable:
           "${process.env.FLIPPER_BROWSER_PORT || ''}".
           Example expected format: "1111".`,
       );
     }
+  }
 
   return {
     serverPorts: portOverrides ?? {