access: make access_GetSize() return an error code

So far, it was returning zero on error. That prevented distinction
between an empty file and a file with unknown size.

include/vlc_access.h

@@ -233,12 +233,9 @@ static inline int access_Control( access_t *p_access, int i_query, ... )
     return i_result;
 }
 
-static inline uint64_t access_GetSize( access_t *p_access )
+static inline int access_GetSize( access_t *p_access, uint64_t *size )
 {
-    uint64_t val;
-    if( access_Control( p_access, ACCESS_GET_SIZE, &val ) )
-        val = 0;
-    return val;
+    return access_Control( p_access, ACCESS_GET_SIZE, size );
 }
 
 static inline void access_InitFields( access_t *p_a )

modules/access/concat.c

@@ -156,8 +156,10 @@ static int Seek(access_t *access, uint64_t position)
         if (!can_seek)
             break;
 
-        uint64_t size = access_GetSize(a);
+        uint64_t size;
 
+        if (access_GetSize(a, &size))
+            size = 0;
         if (position - access->info.i_pos < size)
         {
             if (vlc_access_Seek(a, position - access->info.i_pos))
@@ -281,7 +283,9 @@ static int Open(vlc_object_t *obj)
         if (sys->can_control_pace)
             access_Control(a, ACCESS_CAN_CONTROL_PACE, &sys->can_control_pace);
 
-        sys->size += access_GetSize(a);
+        uint64_t size;
+        if (access_GetSize(a, &size) == 0)
+            sys->size += size;
 
         int64_t caching;
         access_Control(a, ACCESS_GET_PTS_DELAY, &caching);