Better error message when RA custom conditions fail.

src/js/rulesAssistant.js

@@ -151,7 +151,12 @@ globalThis.ruleAppliesP = function(rule, slave) {
 			break;
 		case "custom": // user provided JS function
 			// TODO: This should use a cached Function instead of 'eval'ing
-			flag = eval(cond.data)(slave);
+			try {
+				flag = eval(cond.data)(slave);
+			} catch (e) {
+				// Put together a more useful message for the player. Does mean we are losing the stacktrace.
+				throw new Error(`Rule '${rule.name}' custom condition failed: '${e.message}'`);
+			}
 			break;
 	}
 	if (!flag) {