One line refactor to Packer.h

The refactor changes how the floating point version of unpack()
advances the buffer pointer. The previous implementation did not
cause any known bugs (due to unstated assumptions about the
function's usage), but the newer version is more robust.

runtime/Packer.h

@@ -281,7 +281,7 @@ unpack(const char **in, uint8_t packNibble) {
     T result;
     int bytes = packNibble == 0 ? 16 : packNibble;
     std::memcpy(&result, (*in), bytes);
-    (*in) += sizeof(T);
+    (*in) += bytes;
 
     return result;
 }