Werk #12291: Fix exception on logo upload page (UnsupportedOperation)

Component	Setup
Title	Fix exception on logo upload page (UnsupportedOperation)
Date	Mar 10, 2021
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.1.0b1 Checkmk MSP (CME) 2.0.0p1 Checkmk MSP (CME)

The logo upload / management page failed with an exception (UnsupportedOperation).

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