vorbisdec: support freeing partially allocated contexts.

Fixes null pointer derefernces
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/vorbisdec.c

@@ -195,37 +195,41 @@ static void vorbis_free(vorbis_context *vc)
     av_freep(&vc->channel_residues);
     av_freep(&vc->saved);
 
-    for (i = 0; i < vc->residue_count; i++)
-        av_free(vc->residues[i].classifs);
+    if (vc->residues)
+        for (i = 0; i < vc->residue_count; i++)
+            av_free(vc->residues[i].classifs);
     av_freep(&vc->residues);
     av_freep(&vc->modes);
 
     ff_mdct_end(&vc->mdct[0]);
     ff_mdct_end(&vc->mdct[1]);
 
-    for (i = 0; i < vc->codebook_count; ++i) {
-        av_free(vc->codebooks[i].codevectors);
-        ff_free_vlc(&vc->codebooks[i].vlc);
-    }
+    if (vc->codebooks)
+        for (i = 0; i < vc->codebook_count; ++i) {
+            av_free(vc->codebooks[i].codevectors);
+            ff_free_vlc(&vc->codebooks[i].vlc);
+        }
     av_freep(&vc->codebooks);
 
-    for (i = 0; i < vc->floor_count; ++i) {
-        if (vc->floors[i].floor_type == 0) {
-            av_free(vc->floors[i].data.t0.map[0]);
-            av_free(vc->floors[i].data.t0.map[1]);
-            av_free(vc->floors[i].data.t0.book_list);
-            av_free(vc->floors[i].data.t0.lsp);
-        } else {
-            av_free(vc->floors[i].data.t1.list);
+    if (vc->floors)
+        for (i = 0; i < vc->floor_count; ++i) {
+            if (vc->floors[i].floor_type == 0) {
+                av_free(vc->floors[i].data.t0.map[0]);
+                av_free(vc->floors[i].data.t0.map[1]);
+                av_free(vc->floors[i].data.t0.book_list);
+                av_free(vc->floors[i].data.t0.lsp);
+            } else {
+                av_free(vc->floors[i].data.t1.list);
+            }
         }
-    }
     av_freep(&vc->floors);
 
-    for (i = 0; i < vc->mapping_count; ++i) {
-        av_free(vc->mappings[i].magnitude);
-        av_free(vc->mappings[i].angle);
-        av_free(vc->mappings[i].mux);
-    }
+    if (vc->mappings)
+        for (i = 0; i < vc->mapping_count; ++i) {
+            av_free(vc->mappings[i].magnitude);
+            av_free(vc->mappings[i].angle);
+            av_free(vc->mappings[i].mux);
+        }
     av_freep(&vc->mappings);
 }