forward zlib decompression errors instead of failing hard

lib/mbtiles.js

@@ -231,6 +231,8 @@ MBTiles.prototype.grid = function(x, y, z, callback) {
         function(err, row, rows) {
             if (err) return callback(err);
             if (!row || !row.grid) return callback('Grid does not exist');
+
+            try {
                 var grid = zlib.inflate(
                            !Buffer.isBuffer(row.grid)
                            ? new Buffer(row.grid, 'binary')
@@ -241,6 +243,9 @@ MBTiles.prototype.grid = function(x, y, z, callback) {
                         return memo;
                     }, {});
                 callback(null, _(JSON.parse(grid)).extend({ data: data }));
+            } catch(err) {
+                callback(err);
+            }
         }
     );
 };