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Save current category on update and ignore those launched as dialog or
secondary activity

Close #475

grep was interpreting the variables as regexes intended to
match themselves. this could cause errors or false positives/negatives if the
variables contain regex metacharacters. now the variables are escaped to
produce regexes that will always and only match themselves.

Signed-off-by: Geoffrey Métais <geoffrey.metais@gmail.com>

Allows to be sure if we have video tracks or not