Fix 'weightEvents' with thresholded waves

Since commit 0da5ef7f479e7d096cd961dfbfa4e9f9813adff7 'weightEvents' was
not able to calculate weights from fit results with thresholded waves,
the reading of the amplitudes failed as the filename was "". Fix this by
also adding waves with production amplitude 0 to the list of waves.

(cherry picked from commit 28c70cfc6d1545321b6b50f83769ffea671bccd7)