avutil/buffer: Check ff_mutex_init() for failure

Fixes: CID1604487 Unchecked return value
Fixes: CID1604494 Unchecked return value

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 82f5b20ff5)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/buffer.c

@@ -264,7 +264,10 @@ AVBufferPool *av_buffer_pool_init2(size_t size, void *opaque,
     if (!pool)
         return NULL;
 
-    ff_mutex_init(&pool->mutex, NULL);
+    if (ff_mutex_init(&pool->mutex, NULL)) {
+        av_free(pool);
+        return NULL;
+    }
 
     pool->size      = size;
     pool->opaque    = opaque;
@@ -283,7 +286,10 @@ AVBufferPool *av_buffer_pool_init(size_t size, AVBufferRef* (*alloc)(size_t size
     if (!pool)
         return NULL;
 
-    ff_mutex_init(&pool->mutex, NULL);
+    if (ff_mutex_init(&pool->mutex, NULL)) {
+        av_free(pool);
+        return NULL;
+    }
 
     pool->size     = size;
     pool->alloc    = alloc ? alloc : av_buffer_alloc;