Attach FileReader event handlers before calling its `read*` method
Attach FileReader event handlers before calling its `read*` method

Avoids a potential race condition when the load event already fired
before a handler was attached. This was reported happening in Safari.

Fixes #353

benestudio/fetch,zebulonj/fetch-plus,zebulonj/fetch-plus,JhansiYarnagula/dummy2,JhansiYarnagula/dummy2,benestudio/fetch,zebulonj/fetch-plus,benestudio/fetch,github/fetch,aleclarson/fetch,JhansiYarnagula/dummy2