Merge #19006: rpc: Avoid crash when g_thread_http was never started

faf45d1f1f http: Avoid crash when g_thread_http was never started (MarcoFalke)
fa12a37b27 test: Replace inline-comments with logs, pep8 formatting (MarcoFalke)
fa83b39ff3 init: Remove confusing and redundant InitError (MarcoFalke)

Pull request description:

  Avoid a crash during shutdown when the init sequence failed for some reason

ACKs for top commit:
  promag:
    Tested ACK faf45d1f1f.
  ryanofsky:
    Code review ACK faf45d1f1f. Thanks for updates, this is much easier to parse for me now. Since previous reviews: split out and reverted some cleanups & replaced chmod with mkdir in test
  hebasto:
    ACK faf45d1f1f, tested on Linux Mint 19.3 with the following patch:

Tree-SHA512: 59632bf01c999e65c724e2728ac103250ccd8b0b16fac19d3a2a82639ab73e4f2efb86c78e63c588a5954625d8d0cf9545e2a7e070e6e15d2a54beeb50e00b61

src/httprpc.cpp

@@ -9,7 +9,6 @@
 #include <httpserver.h>
 #include <rpc/protocol.h>
 #include <rpc/server.h>
-#include <ui_interface.h>
 #include <util/strencodings.h>
 #include <util/system.h>
 #include <util/translation.h>
@@ -251,9 +250,6 @@ static bool InitRPCAuthentication()
     {
         LogPrintf("Using random cookie authentication.\n");
         if (!GenerateAuthCookie(&strRPCUserColonPass)) {
-            uiInterface.ThreadSafeMessageBox(
-                _("Error: A fatal internal error occurred, see debug.log for details"), // Same message as AbortNode
-                "", CClientUIInterface::MSG_ERROR);
             return false;
         }
     } else {