Avoid file system access on checking if an image exists

[juliusknorr]

Save some time and potential file system setup when obtaining capabilities (which is done on every template response) for gathering theming capabilities by not getting the background image file but just checking if one is configured.

[nickvergessen]

I see why it was done the old way. But it basically means the cache (appconfig) is not trusted, so it's not helping.

[PVince81]

👍

[PVince81]

1) OCA\Theming\Tests\ImageManagerTest::testGetImageUrl
Expectation failed for method name is "getFolder" when invoked 1 time(s).
Method was expected to be called 1 times, actually called 0 times.

2) OCA\Theming\Tests\ImageManagerTest::testGetImageUrlDefault
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'logo/logo.png?v=0'
+'?v=0'

/drone/src/apps/theming/tests/ImageManagerTest.php:158

3) OCA\Theming\Tests\ImageManagerTest::testGetImageUrlAbsolute
Expectation failed for method name is "getFolder" when invoked 1 time(s).
Method was expected to be called 1 times, actually called 0 times.

@juliushaertl please adjust the tests

[juliusknorr]

Tests adjusted, samba failure unrelated.