Unbreak error logging

Summary:
*Potentially.

A big thanks to lblasa and aigoncharov for helping with debugging. Looking at
`ptail -f errorlog_flipper_javascript` reveals that messages now include a spurious amount of unescaped newlines. E.g. P768993195

From memory, these were not there when I wrote the categorizer when I was able to copy-paste from ptail to the unit tests.

D44729490 added prettifying to the results inadvertently.

Reviewed By: lblasa

Differential Revision: D46685543

fbshipit-source-id: 98da5eff92900042fc5306ca5d5652d8940ff2e1

desktop/flipper-plugin-core/src/utils/safeStringify.tsx

@@ -7,9 +7,9 @@
  * @format
  */
 
-export function safeStringify(value: any) {
+export function safeStringify(value: any, space: number = 2) {
   try {
-    return JSON.stringify(value, null, 2);
+    return JSON.stringify(value, null, space);
   } catch (e) {
     return '<Failed to serialize: ' + e + '>';
   }