Fix bug with MI Parsing if there is a list with empty strings

A JavaScript string is a falsy value - but an empty string is valid in these positions - so need to explicitly check for undefined instead of just falsy.

src/backend/mi_parse.ts

@@ -213,7 +213,7 @@ export function parseMI(output: string): MINode {
 				let values = [];
 				values.push(value);
 				let remaining = output;
-				while (value = parseCommaValue())
+				while ((value = parseCommaValue()) !== undefined)
 					values.push(value);
 				output = output.substr(1); // ]
 				return values;