getLayerBaseUrl does not work for string literals

[hbruch]

In line mapLayerUtils.getLayerBaseUrl the check urlOrUrlMap instanceof String returns false for string literals and should be replaced by e.g. typeof urlOrUrlMap === 'string'.

There might be further occurences where such a check might fail.

[vesameskanen]

grep -r 'instanceof' app
app/util/legUtils.js: typeof legOrMode === 'string' || legOrMode instanceof String
app/util/modeUtils.js: const modesStr = modes instanceof Array ? modes.join(',') : modes;
app/util/mapLayerUtils.js: return urlOrUrlMap instanceof String
app/util/mqttClient.js: if (message instanceof Uint8Array) {

[vesameskanen]

One check does the both :)