Bug fix - an error in the PDML loader left the process running

If the running platform does not have /proc/pid/fdinfo support, the
spinner is used during loading, and this bug leaves the spinner running
indefinitely if there is an error in the generated PDML. I see such an
error on macOS with tshark 3.4.4:

<field name="irc.response" showname="Response: :Samsung.US.SPUNet.org NOTICE Auth :Welcome to \002SPUNet\002!" size="56" pos="54" show=":Samsung.US.SPUNet.org NOTICE Auth :Welcome to �SPUNet�!" value="3a53616d73756e672e55532e5350554e65742e6f7267204e4f544943452041757468203a57656c636f6d6520746f20025350554e65740221">

The 0x02 bytes surrounding SPUNet are not handled by the Go XML parser.

pcap/loader.go

@@ -1086,6 +1086,8 @@ func (c *PdmlLoader) loadPcapSync(row int, visible bool, ps iPdmlLoaderEnv, cb i
 				if err != nil {
 					if !issuedKill && unexpectedPdmlError(err) {
 						err = fmt.Errorf("Could not read PDML data: %v", err)
+						issuedKill = true
+						pdmlCancelFn()
 						HandleError(PdmlCode, app, err, cb)
 					}
 					if err == io.EOF {
@@ -1101,6 +1103,8 @@ func (c *PdmlLoader) loadPcapSync(row int, visible bool, ps iPdmlLoaderEnv, cb i
 						if err != nil {
 							if !issuedKill && unexpectedPdmlError(err) {
 								err = fmt.Errorf("Could not decode PDML data: %v", err)
+								issuedKill = true
+								pdmlCancelFn()
 								HandleError(PdmlCode, app, err, cb)
 							}
 							break Loop