Capture available data early

The availableData object should be captured in the event
handler. If you delay reading the data to the synchronization
queue, the socket may be closed already (leading to an
ObjC exception you can't catch).

Author: helje5

Sources/ShellOut.swift

@@ -367,16 +367,16 @@ private extension Process {
 
         #if !os(Linux)
         outputPipe.fileHandleForReading.readabilityHandler = { handler in
+            let data = handler.availableData
             outputQueue.async {
-                let data = handler.availableData
                 outputData.append(data)
                 outputHandle?.write(data)
             }
         }
 
         errorPipe.fileHandleForReading.readabilityHandler = { handler in
+            let data = handler.availableData
             outputQueue.async {
-                let data = handler.availableData
                 errorData.append(data)
                 errorHandle?.write(data)
             }