Move ff_dct_init(context) out of if(one time init)

fixes calling a null pointer in issue658

Originally committed as revision 24081 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegaudiodec.c

@@ -323,6 +323,9 @@ static av_cold int decode_init(AVCodecContext * avctx)
     s->apply_window_mp3 = apply_window_mp3_c;
 #if HAVE_MMX && CONFIG_FLOAT
     ff_mpegaudiodec_init_mmx(s);
+#endif
+#if CONFIG_FLOAT
+    ff_dct_init(&s->dct, 5, DCT_II);
 #endif
     if (HAVE_ALTIVEC && CONFIG_FLOAT) ff_mpegaudiodec_init_altivec(s);
 
@@ -356,9 +359,6 @@ static av_cold int decode_init(AVCodecContext * avctx)
                     scale_factor_mult[i][2]);
         }
 
-#if CONFIG_FLOAT
-        ff_dct_init(&s->dct, 5, DCT_II);
-#endif
         RENAME(ff_mpa_synth_init)(RENAME(ff_mpa_synth_window));
 
         /* huffman decode tables */