core: fix py3 for no detections

src/core.py

@@ -413,9 +413,9 @@ def search(
                 num.max(ydata_window),
                 num.median(ydata_window)))
 
-            tpeaks, apeaks = zip(*[(tpeak, apeak) for (tpeak, apeak) in zip(
+            tpeaks, apeaks = list(zip(*[(tpeak, apeak) for (tpeak, apeak) in zip(
                 *tr_stackmax.peaks(config.detector_threshold, tpeaksearch)) if
-                wmin <= tpeak and tpeak < wmax]) or ([], [])
+                wmin <= tpeak and tpeak < wmax])) or ([], [])
 
             tr_stackmax_indx = tr_stackmax.copy(data=False)