reject of combinedImage is eaten

[yykoypj]

Rejection in the combineImages will not be passed to ouside, which may happend all the time.

        convertPromise.then(function(imagePaths){
          if (pdfImage.combinedImage){
            pdfImage.combineImages(imagePaths).then(function(imagePath){
              resolve(imagePath);
            });
          } else {
            resolve(imagePaths);
          }
        }).catch(function(error){
          reject(error);
        });