Loaders: Add cancelation to all file loaders.

Mainly, for HTTP which might be stalled trying to connect (especially if
you're not near your PC right now and it's in your recent, for example.)

Core/FileLoaders/HTTPFileLoader.cpp

@@ -22,7 +22,7 @@
 #include "Core/FileLoaders/HTTPFileLoader.h"
 
 HTTPFileLoader::HTTPFileLoader(const std::string &filename)
-	: filesize_(0), filepos_(0), url_(filename), filename_(filename), connected_(false) {
+	: url_(filename), filename_(filename) {
 }
 
 void HTTPFileLoader::Prepare() {
@@ -33,6 +33,10 @@ void HTTPFileLoader::Prepare() {
 		}
 
 		Connect();
+		if (!connected_) {
+			return;
+		}
+
 		int err = client_.SendRequest("HEAD", url_.Resource().c_str());
 		if (err < 0) {
 			Disconnect();
@@ -123,6 +127,9 @@ size_t HTTPFileLoader::ReadAt(s64 absolutePos, size_t bytes, void *data, Flags f
 	}
 
 	Connect();
+	if (!connected_) {
+		return 0;
+	}
 
 	char requestHeaders[4096];
 	// Note that the Range header is *inclusive*.
@@ -186,3 +193,11 @@ size_t HTTPFileLoader::ReadAt(s64 absolutePos, size_t bytes, void *data, Flags f
 	filepos_ = absolutePos + readBytes;
 	return readBytes;
 }
+
+void HTTPFileLoader::Connect() {
+	if (!connected_) {
+		cancelConnect_ = false;
+		// Latency is important here, so reduce the timeout.
+		connected_ = client_.Connect(3, 10.0, &cancelConnect_);
+	}
+}