Protocol: add type check

Fixes: #1059

Author: mscdex

lib/protocol/Protocol.js

@@ -1669,6 +1669,9 @@ class Protocol {
 
     const origSignal = name;
 
+    if (typeof origSignal !== 'string' || !origSignal)
+      throw new Error(`Invalid signal: ${origSignal}`);
+
     let signal = name.toUpperCase();
     if (signal.slice(0, 3) === 'SIG')
       signal = signal.slice(3);