Truncated WT Files no longer add noise

Truncated WT files would silently fill the end of the buffer
with noise. This was actually a problem for oneshot/Pulse
which advertises 3 tables but has 2. Clearly some old
semantic where this would have worked is either ignore the
last or fill with zero, so replace the fixme which was sitting
here with a fill-with-zero. This will also fix
surge-synthesizer/surge-rack#843 when all
merged through.

src/common/SurgeStorage.cpp

@@ -1229,7 +1229,19 @@ bool SurgeStorage::load_wt_wt(string filename, Wavetable *wt)
 
     const std::unique_ptr<char[]> data{new char[ds]};
     read = f.sgetn(data.get(), ds);
-    // FIXME - error if read != ds
+
+    if (read != ds)
+    {
+        /* Somehow the file is corrupt. We have a few options
+         * including throw an error here but I think
+         * the best thing to do is just zero pad. In the
+         * factory set, the 'OneShot/Pulse' wavetable
+         * has this problem as a future test case.
+         */
+        auto dpad = data.get() + read;
+        auto drest = ds - read;
+        memset(dpad, 0, drest);
+    }
 
     waveTableDataMutex.lock();
     bool wasBuilt = wt->BuildWT(data.get(), wh, false);