Invalid statement when no extension is loaded in Nim.
When no extension is selected for loading glad generates an emtpy var section, which is illegal in Nim.
`findExtensionsGL` needs a discard statement when it is empty.

```nim
# Extensions
var
  # without a single entry this is illegal

#[...]#

proc findExtensionsGL() =
  discard
```

Alternatively if you do not want to treat _no extensions_ as a special case, you can give each variable it's own var section and add a doc comment to `findExtensionsGL`.

```nim
var GLAD_GL_ARB_bindless_texture*: bool
var GL_UNSIGNED_INT64_ARB*: GLenum = GLenum(0x140F)
var GLAD_GL_ARB_direct_state_access*: bool
var GL_TEXTURE_TARGET*: GLenum = GLenum(0x1006)
var GL_QUERY_TARGET*: GLenum = GLenum(0x82EA)
var GL_TEXTURE_BINDING_CUBE_MAP_ARRAY*: GLenum = GLenum(0x900A)

#[...]#

proc findExtensionsGL() =
  ## Some doc comment to make this valid even when it is empty. But it is probably 
  ## better if you put a real meaningful doc comment here.
  GLAD_GL_ARB_bindless_texture = hasExt("GL_ARB_bindless_texture")
  GLAD_GL_ARB_direct_state_access = hasExt("GL_ARB_direct_state_access")
```


