[1.8.x] Fixed #24802 -- Delayed GDAL check for OSMGeoAdmin

# Getting the normal admin routines, classes, and `site` instance.

from django.contrib.admin import (  # NOQA: flake8 detects only the last __all__

from django.contrib.admin import (

    autodiscover, site, AdminSite, ModelAdmin, StackedInline, TabularInline,

    HORIZONTAL, VERTICAL,

)

# Geographic admin options classes and widgets.

from django.contrib.gis.admin.options import GeoModelAdmin      # NOQA

from django.contrib.gis.admin.widgets import OpenLayersWidget   # NOQA

from django.contrib.gis.admin.options import GeoModelAdmin, OSMGeoAdmin

from django.contrib.gis.admin.widgets import OpenLayersWidget

__all__ = [

    "autodiscover", "site", "AdminSite", "ModelAdmin", "StackedInline",

    "TabularInline", "HORIZONTAL", "VERTICAL",

    "GeoModelAdmin", "OpenLayersWidget", "HAS_OSM",

    'autodiscover', 'site', 'AdminSite', 'ModelAdmin', 'StackedInline',

    'TabularInline', 'HORIZONTAL', 'VERTICAL', 'GeoModelAdmin', 'OSMGeoAdmin',

    'OpenLayersWidget',

]

try:

    from django.contrib.gis.admin.options import OSMGeoAdmin

    HAS_OSM = True

    __all__ += ['OSMGeoAdmin']

except ImportError:

    HAS_OSM = False

from django.contrib.gis.admin.widgets import OpenLayersWidget

from django.contrib.gis.db import models

from django.contrib.gis.gdal import HAS_GDAL, OGRGeomType

from django.core.exceptions import ImproperlyConfigured

spherical_mercator_srid = 3857

class GeoModelAdmin(ModelAdmin):

                      }

        return OLMap

if HAS_GDAL:

    spherical_mercator_srid = 3857

class OSMGeoAdmin(GeoModelAdmin):

    map_template = 'gis/admin/osm.html'

    max_resolution = '156543.0339'

    point_zoom = num_zoom - 6

    units = 'm'

    def __init__(self, *args):

        if not HAS_GDAL:

            raise ImproperlyConfigured("OSMGeoAdmin is not usable without GDAL libs installed")

        super(OSMGeoAdmin, self).__init__(*args)

from django.contrib.gis import admin

from django.contrib.gis.db import models

from django.contrib.gis.gdal import HAS_GDAL

from django.utils.encoding import python_2_unicode_compatible

    def __str__(self):

        return self.name

if HAS_GDAL:

    admin.site.register(City, admin.OSMGeoAdmin)