Mariadb processes stuck after aborted dump restore. What to do?
you can kill the mysqld.exe process  

taskkill /im mysqld.exe /f

from the elevated command prompt. Then start service again.
But before you do this, it would be nice of you to take a process dump (with procdump for example, e.g procdump -mp mysqld.exe) , and file a bug in mariadb bug tracker https://jira.mariadb.org , attaching the dump.