services/horizon: Improve error handling for when stellar-core crashes

ingest/ledgerbackend/captive_core_backend.go

@@ -572,16 +572,16 @@ func (c *CaptiveStellarCore) checkMetaPipeResult(result metaResult, ok bool) err
 		return err
 	}
 	if !ok || result.err != nil {
-		if result.err != nil {
-			// Case 3 - Some error was encountered while consuming the ledger stream emitted by captive core.
-			return result.err
-		} else if exited, err := c.stellarCoreRunner.getProcessExitError(); exited {
+		if exited, err := c.stellarCoreRunner.getProcessExitError(); exited {
 			// Case 2 - The stellar core process exited unexpectedly
 			if err == nil {
 				return errors.Errorf("stellar core exited unexpectedly")
 			} else {
 				return errors.Wrap(err, "stellar core exited unexpectedly")
 			}
+		} else if result.err != nil {
+			// Case 3 - Some error was encountered while consuming the ledger stream emitted by captive core.
+			return result.err
 		} else if !ok {
 			// This case should never happen because the ledger buffer channel can only be closed
 			// if and only if the process exits or the context is canceled.

ingest/ledgerbackend/captive_core_backend_test.go

@@ -899,6 +899,7 @@ func TestCaptiveGetLedger_ErrReadingMetaResult(t *testing.T) {
 	mockRunner.On("close").Return(nil).Run(func(args mock.Arguments) {
 		cancel()
 	}).Once()
+	mockRunner.On("getProcessExitError").Return(false, nil)
 
 	// even if the request to fetch the latest checkpoint succeeds, we should fail at creating the subprocess
 	mockArchive := &historyarchive.MockArchive{}