Issue #1862892 by oriol_e9g, joseph.olstad, vaplas, G.I.Joe, leopathu,...

Issue #1862892 by oriol_e9g, joseph.olstad, vaplas, G.I.Joe, leopathu, peterpoe, cilefen, xjm, larowlan: When a theme has a managed_file field and a submit callback, call to undefined function error is thrown

(cherry picked from commit 7f9287e8)