Prevent double-submission of report generation requests
Prevent double-submission of report generation requests

The wrong event object was having its `preventDefault` called, which
led to multiple requests being sent when a button was pressed to submit
a form for generating a report.

flag = none

refs FOO-2576

test plan: Generate any account level report. Wait until the report
is done. Check the reports API and verify only one report is generated.

Change-Id: I0ce83f218c5d0b0357c9dca9e96e1e97aaf37fca
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/280636
Reviewed-by: Charley Kline <05950d7e90ba5e3da323378368c22b3ffaaf6647@instructure.com>
Product-Review: Charley Kline <05950d7e90ba5e3da323378368c22b3ffaaf6647@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: Sean Scally <ceb34b930afeb707ad0575cfce0e31dce3c15014@instructure.com>

instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms