fix whole-wildcard and short prefix globs in determine_filter_type

[aizu-m]

Setting the select filter to the whole-wildcard form leaves no usable driver:

$ VK_LOADER_DRIVERS_SELECT='**' ./vulkaninfo
[Vulkan Loader] WARNING | DRIVER: Driver "ABC_ICD.json" ignored because not selected by env var 'VK_LOADER_DRIVERS_SELECT'
[Vulkan Loader] WARNING | DRIVER: Driver "BCD_ICD.json" ignored because not selected by env var 'VK_LOADER_DRIVERS_SELECT'
vkCreateInstance: VK_ERROR_INCOMPATIBLE_DRIVER

Found this reading determine_filter_type for something unrelated. ** is one of the three
whole-wildcard forms next to * and ~all~, so it should have matched every name.

Both branches that classify a token as FILTER_STRING_SPECIAL assign the type and then fall
through into the star_begin/star_end classification below, which overwrites it. ** comes out
as a suffix filter on *, and no manifest or layer name ends in a star. The filter_length == 2
test also never checked the leading character, so a two character glob like A* took that same
branch and ended up FILTER_STRING_FULLNAME on the literal A* rather than a prefix on A.

Worth noting the disable direction fails open: VK_LOADER_LAYERS_DISABLE=** sets neither
disable_all nor a filter that can match, so every layer stays enabled.

Returning once a token is classified special, and requiring the leading star for the two
character case, fixes both. Every other glob form classifies exactly as before.

[ci-tester-lunarg]

Author aizu-m not on autobuild list. Waiting for curator authorization before starting CI build.

[ci-tester-lunarg]

Author aizu-m not on autobuild list. Waiting for curator authorization before starting CI build.