Handling exceptions in IDE main to avoid entering "zombie process" state. (#3648)

This is meant to address https://www.pivotaltracker.com/story/show/182691027.

CHANGELOG.md

@@ -54,6 +54,9 @@
   methods, atoms and functions are presented in nice, categorized view. The most
   popular tools are available at hand. The The panel is unstable, and thus is
   available under the `--enable-new-component-browser` flag.
+- [Fixed error handling during startup.][3648] This prevents entering IDE into a
+  "zombie" state, where processes were started but not visible to user. They
+  could cause issues with starting further IDE instances.
 
 #### EnsoGL (rendering engine)
 
@@ -273,6 +276,7 @@
 [3601]: https://github.com/enso-org/enso/pull/3601
 [3617]: https://github.com/enso-org/enso/pull/3617
 [3629]: https://github.com/enso-org/enso/pull/3629
+[3648]: https://github.com/enso-org/enso/pull/3648
 
 #### Enso Compiler
 

app/ide-desktop/lib/client/src/index.js

@@ -476,7 +476,10 @@ let mainWindow = null
 let origin = null
 
 async function main(args) {
+    // Note [Main error handling]
+    try {
         runBackend()
+
         console.log('Starting the IDE service.')
         if (args.server !== false) {
             let serverCfg = Object.assign({}, args)
@@ -495,7 +498,23 @@ async function main(args) {
                 }
             })
         }
+    } catch (err) {
+        // Note [Main error handling]
+        console.error('Failed to setup IDE. Error:', err)
+        Electron.app.quit()
     }
+}
+
+// Note [Main error handling]
+// ==========================
+// It is critical that the main function runs in its entirety. Otherwise, IDE enters a "zombie
+// process" state, where Electron processes have been spawned, but there is no window and user can't
+// observe anything. Usually they will try to spawn another instance of the IDE, but this can fail
+// because of these zombie process presence.
+//
+// The solution is to catch all errors and exit the process if any part of the initial setup fails.
+// If it succeeds, at least the Window will be shown, allowing the user to observe the error and
+// close it.
 
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     let params = []