[BUGFIX] Extensionmanager: Dependency errors are not reset

Due to changes in https://review.typo3.org/#/c/29845/ dependency errors
are collected and if one error occurred it is returned for every check
regardless of the key. This patch adds a reset for the error array on
every new dependency check.

Resolves: #60106
Releases: 6.3, 6.2
Change-Id: Id734ba1fe8981ffd270d79d4971ac9de9b72b4b4
Reviewed-on: https://review.typo3.org/31383
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn