Net: three smaller fixes from reviewing the server code

RequestHeader::GetParamValue indexed parts[1] without checking the size. A query
parameter with no '=' at all ("?foo") makes SplitString return a single element, so
both the DEBUG_LOG and the assignment read off the end of the vector. Nothing calls
GetParamValue today, so this is latent rather than live, but it's driven straight
off the request line.

The 64-bit frame length was assembled with header[n] << 24 on uint8_t values, which
promote to int - a byte >= 0x80 in the top position shifts into the sign bit and then
sign-extends when widened to uint64_t. The resulting size was always rejected, just
by the wrong check and via signed overflow to get there. Cast first.

OutputSink::Block() had the same shape as the InputSink one this branch already
fixed: a broken socket is reported ready immediately and forever, so waiting on it
is a spin. Bail if the sink already knows it's broken.

Common/Net/WebsocketServer.cpp

@@ -400,9 +400,10 @@ bool WebSocketServer::ReadFrame() {
 			return false;
 
 		mask = &header[10];
-		// Read from big endian.
-		uint64_t high = (header[2] << 24) | (header[3] << 16) | (header[4] << 8) | (header[5] << 0);
-		uint64_t low = (header[6] << 24) | (header[7] << 16) | (header[8] << 8) | (header[9] << 0);
+		// Read from big endian. Cast first: these promote to int, so a byte >= 0x80 in the top
+		// position would shift into the sign bit and then sign-extend into the u64.
+		uint64_t high = ((uint64_t)header[2] << 24) | ((uint64_t)header[3] << 16) | ((uint64_t)header[4] << 8) | (uint64_t)header[5];
+		uint64_t low = ((uint64_t)header[6] << 24) | ((uint64_t)header[7] << 16) | ((uint64_t)header[8] << 8) | (uint64_t)header[9];
 		sz = (high << 32) | low;
 
 		if ((sz & 0x8000000000000000ULL) != 0) {