[7.4] [ML] Data frame analytics: Fix source index checks. (#44479)#44595

Merged

walterra merged 1 commit intoelastic:7.4from walterra:backport/7.4/pr-44479

Sep 2, 2019

+30-43

Commits on Sep 2, 2019

[ML] Data frame analytics: Fix source index checks. (elastic#44479 )
walterra
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