libavcenc: return partially encoded buffer for application

As bitstream overflow errors are not marked as fatal errors and
these recons are being used for reference, its best to return
the partial encoded buffers for application

Change-Id: I30a8e9907cf42d3bc883ee78b28cbae723bad7ac

encoder/ih264e_error.h

@@ -48,7 +48,7 @@
     {\
         out_status = ((1 << severity) | error);\
         ps_codec->i4_error_code = out_status;\
-        return (ret_code);\
+        if (severity == IVE_FATALERROR) return (ret_code);\
     }