Fix -Wsign-compare warnings.

I decided to modify code in a defensive way. Ideally functions
like size() or length() should return an unsigned type.

core/io/packet_peer.cpp

@@ -224,7 +224,7 @@ Error PacketPeerStream::get_packet(const uint8_t **r_buffer, int &r_buffer_size)
 	uint32_t len = decode_uint32(lbuf);
 	ERR_FAIL_COND_V(remaining < (int)len, ERR_UNAVAILABLE);
 
-	ERR_FAIL_COND_V(input_buffer.size() < len, ERR_UNAVAILABLE);
+	ERR_FAIL_COND_V(input_buffer.size() < (int)len, ERR_UNAVAILABLE);
 	ring_buffer.read(lbuf, 4); //get rid of first 4 bytes
 	ring_buffer.read(input_buffer.ptrw(), len); // read packet
 

core/io/resource_format_binary.cpp

@@ -106,7 +106,7 @@ StringName ResourceInteractiveLoaderBinary::_get_string() {
 	uint32_t id = f->get_32();
 	if (id & 0x80000000) {
 		uint32_t len = id & 0x7FFFFFFF;
-		if (len > str_buf.size()) {
+		if ((int)len > str_buf.size()) {
 			str_buf.resize(len);
 		}
 		if (len == 0)