bug 1223520 avoid leaking NaNs to and from the otherwise unused imaginary frequency components r=padenot

The zeroth component is not removed from the BufferComplexMultiply() call so
as not to disrupt alignment.

The mOutputBuffer[halfSize].i assertions are removed because the code no
longer uses these components, and so their values are irrelevant.

--HG--
extra : rebase_source : 96014bdb66a86e1d764979f7b1a313c24196a60b
extra : histedit_source : 59ef41301d48a7f80798d8dbecc43aa85703c26f

dom/media/webaudio/FFTBlock.h

@@ -138,14 +138,15 @@ public:
     uint32_t halfSize = mFFTSize / 2;
     // DFTs are not packed.
     MOZ_ASSERT(mOutputBuffer[0].i == 0);
-    MOZ_ASSERT(mOutputBuffer[halfSize].i == 0);
     MOZ_ASSERT(aFrame.mOutputBuffer[0].i == 0);
-    MOZ_ASSERT(aFrame.mOutputBuffer[halfSize].i == 0);
 
     BufferComplexMultiply(mOutputBuffer.Elements()->f,
                           aFrame.mOutputBuffer.Elements()->f,
                           mOutputBuffer.Elements()->f,
-                          halfSize + 1);
+                          halfSize);
+    mOutputBuffer[halfSize].r *= aFrame.mOutputBuffer[halfSize].r;
+    // This would have been set to NaN if either real component was NaN.
+    mOutputBuffer[0].i = 0.0f;
   }
 
   // Perform a forward FFT on |aData|, assuming zeros after dataSize samples,