ft4: Initialize uninitialized decoder members

cppcheck reported uninitialized scalar members in the FT4 constructor.
Initialize pass_ and cached sample values hack_0_ and hack_1_ to avoid
undefined behavior when these members are used before assignment.

Signed-off-by: Robin Getz <rgetz503@gmail.com>

ft8/ft4.cpp

@@ -122,6 +122,9 @@ FT4::FT4(
     hack_len_ = -1;
     fftEngine_ = fftEngine;
     npasses_ = 1;
+    pass_ = 0;
+    hack_0_ = 0.0f;
+    hack_1_ = 0.0f;
 }
 
 void FT4::start_work()