Call exitValue only if process completed

Otherwise this will throw an exception, making the check for completion
irrelevant and possibly leaving a dangling process.

Author: hinerm

src/main/java/net/imagej/ui/swing/updater/LauncherMigrator.java

@@ -534,11 +534,11 @@ private static List<String> collectProcessOutput(Process p)
 		throws IOException, InterruptedException
 	{
 		boolean completed = p.waitFor(5, TimeUnit.SECONDS);
-		p.exitValue();
 		if (!completed) {
 			p.destroyForcibly();
 			throw new IOException("Process took too long to complete.");
 		}
+		p.exitValue();
 		try (BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()))) {
 			return reader.lines().collect(Collectors.toList());
 		}