Check that the SBR decoder has been properly initialized

This probably doesn't fix the root cause, but at least fixes
the issues found in this particular fuzzed sample.

Fixes: 1994/clusterfuzz-testcase-minimized-6368089497141248

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg

libSBRdec/src/sbr_dec.cpp

@@ -940,6 +940,10 @@ resetSbrDec (HANDLE_SBR_DEC hSbrDec,
   FIXP_DBL  **OverlapBufferReal = hSbrDec->QmfBufferReal;
   FIXP_DBL  **OverlapBufferImag = hSbrDec->QmfBufferImag;
 
+  if (!hSbrDec->LppTrans.pSettings) {
+    return SBRDEC_NOT_INITIALIZED;
+  }
+
   /* assign qmf time slots */
   assignTimeSlots( hSbrDec, hHeaderData->numberTimeSlots * hHeaderData->timeStep, useLP);