Run clearCaches synchronously to prevent _commit from erroring out when called prior to startWriting completing.

lib/mbtiles.js

@@ -398,6 +398,7 @@ MBTiles.prototype.startWriting = function(callback) {
     if (!this.open) return callback(new Error('MBTiles not yet loaded'));
 
     var mbtiles = this;
+    mbtiles._clearCaches();
     Step(function() {
         mbtiles._setup(this);
     }, function(err) {
@@ -406,7 +407,6 @@ MBTiles.prototype.startWriting = function(callback) {
         // See http://www.sqlite3.org/pragma.html#pragma_synchronous
         if (!mbtiles._isWritable) {
             mbtiles._isWritable = 1;
-            mbtiles._clearCaches();
             mbtiles._db.run('PRAGMA synchronous=OFF', this);
         } else {
             mbtiles._isWritable++;