Only set afterType when a token is recognized as a keyword

[jeffbolznv]

Fixes #4139.

I did this for most existing keywords, but not for the sampler stuff because the logic is somewhat different and there are some existing warnings that it raises.

[jeroenbakker-atmind]

This PR seems to fix the issue. (tested a single shader)

Current main

$ ./glslang ./overlay_volume_velocity_needle.vert.glsl --target-env vulkan1.2
./overlay_volume_velocity_needle.vert.glsl
ERROR: overlay_volume_velocity_vert.glsl:59: 'vector' : undeclared identifier 
ERROR: overlay_volume_velocity_vert.glsl:59: '' : compilation terminated 
ERROR: 2 compilation errors.  No code generated.


ERROR: Linking vertex stage: No function definition (body) found: 
    main_function_(

SPIR-V is not generated for failed compile or link

With PR

$ ./glslang ./overlay_volume_velocity_needle.vert.glsl --target-env vulkan1.2
./overlay_volume_velocity_needle.vert.glsl
$

[dnovillo]

Thanks. LGTM.