[C] aeron_properties_load should not fail on non-existing file/resource

The Java side uses `org.agrona.SystemUtil#loadPropertiesFiles(java.lang.String...)` API which ignores non-existing files/resources. However the C implementation of the `aeron_properties_file_load` fails with error if file cannot be opened. This leads to media driver failing to start if executed from a script that points to some default files (e.g. `c-media-driver` script from the benchmarks project).