[telemetry] fix segfault (#1569)

## Summary

`newSentryException` can error
[here](https://github.com/jetpack-io/devbox/blob/main/internal/telemetry/sentry.go#L55)
due to `err` being `nil`. Its only callsite is
[here](https://github.com/jetpack-io/devbox/blob/main/internal/telemetry/telemetry.go#L130),
but the `nix.Version` above is resetting the `err` to `nil` leading to a
segfault.

This was my bad from #1469 

In this PR, I change the variable `err` to `errToLog` so that any of us
adding other code here do not accidentally clobber the `errToLog`
variable.

I think but not sure this is the cause of #1562 (but not sure).

## How was it tested?

I managed to get a repro with the nginx example and running `devbox`
version 0.6, and doing `devbox services up -b`, when the services are
already running leading to an error.

When I run it with the new `devbox` binary, it errors correctly without
a segfault.

Author: savil

internal/telemetry/sentry.go

@@ -51,8 +51,8 @@ func initSentryClient(appName string) bool {
 	return err == nil
 }
 
-func newSentryException(err error) []sentry.Exception {
-	errMsg := err.Error()
+func newSentryException(errToLog error) []sentry.Exception {
+	errMsg := errToLog.Error()
 	binPkg := ""
 	modPath := ""
 	if build, ok := debug.ReadBuildInfo(); ok {
@@ -66,12 +66,12 @@ func newSentryException(err error) []sentry.Exception {
 	var stFunc func() []runtime.Frame
 	errType := "Generic Error"
 	for {
-		if t := exportedErrType(err); t != "" {
+		if t := exportedErrType(errToLog); t != "" {
 			errType = t
 		}
 
 		//nolint:errorlint
-		switch stackErr := err.(type) {
+		switch stackErr := errToLog.(type) {
 		// If the error implements the StackTrace method in the redact package, then
 		// prefer that. The Sentry SDK gets some things wrong when guessing how
 		// to extract the stack trace.
@@ -98,11 +98,11 @@ func newSentryException(err error) []sentry.Exception {
 				return frames
 			}
 		}
-		uw := errors.Unwrap(err)
+		uw := errors.Unwrap(errToLog)
 		if uw == nil {
 			break
 		}
-		err = uw
+		errToLog = uw
 	}
 	ex := []sentry.Exception{{Type: errType, Value: errMsg}}
 	if stFunc != nil {

internal/telemetry/telemetry.go

@@ -114,7 +114,8 @@ func commandEvent(meta Metadata) (id string, msg *segment.Track) {
 
 // Error reports an error to the telemetry server.
 func Error(err error, meta Metadata) {
-	if !started || err == nil {
+	errToLog := err // use errToLog to avoid shadowing err later. Use err to keep API clean.
+	if !started || errToLog == nil {
 		return
 	}
 
@@ -127,7 +128,7 @@ func Error(err error, meta Metadata) {
 		EventID:   sentry.EventID(ExecutionID),
 		Level:     sentry.LevelError,
 		User:      sentry.User{ID: deviceID},
-		Exception: newSentryException(redact.Error(err)),
+		Exception: newSentryException(redact.Error(errToLog)),
 		Contexts: map[string]map[string]any{
 			"os": {
 				"name": build.OS(),

internal/telemetry/telemetry_test.go

@@ -0,0 +1,19 @@
+package telemetry
+
+import (
+	"errors"
+	"testing"
+)
+
+// TestErrorBasic does a very simple sanity check to ensure the error can be sent
+// to the sentry and segment buffers
+func TestErrorBasic(t *testing.T) {
+	segmentBufferDir = t.TempDir()
+	sentryBufferDir = t.TempDir()
+	started = true
+
+	fakeErr := errors.New("fake error")
+	meta := Metadata{}
+
+	Error(fakeErr, meta)
+}