fix(PIFileTransfer): validate file id before array access

processFile() accessed files_[id - 1] without validating id.
When id == 0 (from a crafted network packet), id - 1 = -1 caused
out-of-bounds access. Added bounds check: id must be in range
[1, files_.size()]. Stops receive and logs error on invalid id.

libs/main/io_utils/pifiletransfer.cpp

@@ -131,6 +131,12 @@ bool PIFileTransfer::sendFiles(const PIVector<PFTFileInfo> & files) {
 
 void PIFileTransfer::processFile(int id, ullong start, PIByteArray & data) {
 	// piCout << "processFile" << id << files_.size();
+	if (id <= 0 || id > files_.size_s()) {
+		cur_file_string = "Error: Invalid file id " + PIString::fromNumber(id);
+		piCoutObj << cur_file_string;
+		stopReceive();
+		return;
+	}
 	PFTFileInfo fi  = files_[id - 1];
 	bytes_file_all  = fi.size;
 	bytes_file_cur  = start;