bugfix of r4086: nginx could not be built without debug log.
diff --git a/src/http/modules/ngx_http_mp4_module.c b/src/http/modules/ngx_http_mp4_module.c
index c5997c5..804448f 100644
--- a/src/http/modules/ngx_http_mp4_module.c
+++ b/src/http/modules/ngx_http_mp4_module.c
@@ -704,7 +704,7 @@
                  + ngx_http_mp4_update_mdat_atom(mp4, start_offset)
                  - start_offset;
 
-    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
+    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
                    "mp4 adjustment:%D", adjustment);
 
     for (i = 0; i < mp4->trak.nelts; i++) {
@@ -794,7 +794,7 @@
 
         atom_name = atom_header + sizeof(uint32_t);
 
-        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
+        ngx_log_debug4(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
                        "mp4 atom: %*s @%O:%uL",
                        4, atom_name, mp4->offset, atom_size);
 
@@ -1026,7 +1026,7 @@
     mp4->mdat_data.buf->file_pos = start_offset;
     mp4->content_length += atom_data_size;
 
-    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
+    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
                    "mdat new offset @%O:%O", start_offset, atom_data_size);
 
     atom_header = mp4->mdat_atom_header;
@@ -2109,7 +2109,7 @@
     while (entry < end) {
         count = ngx_mp4_get_32value(entry->count);
 
-        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
+        ngx_log_debug3(NGX_LOG_DEBUG_HTTP, mp4->file.log, 0,
                        "start:%uD, count:%uD, offset:%uD",
                        start_sample, count, ngx_mp4_get_32value(entry->offset));