Fix potential division by zero in stratum target calculation, Refactored the nested division expression, intermediate variables with safety checks, prevents potential undefined

behavior that was causing UBSAN crashes

src/stratum_server.cpp

@@ -438,7 +438,13 @@ bool StratumServer::on_submit(StratumClient* client, uint32_t id, const char* jo
 
 		if (target >= TARGET_4_BYTES_LIMIT) {
 			// "Low diff share" fix: adjust target to the same value as XMRig would use
-			target = std::numeric_limits<uint64_t>::max() / (std::numeric_limits<uint32_t>::max() / (target >> 32));
+			const uint64_t upper_bits = target >> 32;
+			if (upper_bits > 0) {
+				const uint64_t divisor = std::numeric_limits<uint32_t>::max() / upper_bits;
+				if (divisor > 0) {
+					target = std::numeric_limits<uint64_t>::max() / divisor;
+				}
+			}
 		}
 
 		SubmittedShare share{};