Fix missing fallback for shader precaching

Author: BMagnu

code/def_files/data/effects/shadow_map-v.sdr

@@ -2,7 +2,7 @@
 #extension GL_ARB_gpu_shader5: enable
 
 #ifndef GEOMETRY_FALLBACK
-#extension GL_ARB_shader_viewport_layer_array : require
+#extension GL_ARB_shader_viewport_layer_array : enable
 #endif
 
 in vec4 vertPosition;

code/model/modelread.cpp

@@ -3208,7 +3208,7 @@ void model_load_texture(polymodel *pm, int i, const char *file)
 
 	// See if we need to compile a new shader for this material
 	if (Shadow_quality != ShadowQuality::Disabled)
-		gr_maybe_create_shader(SDR_TYPE_SHADOW_MAP_GEN, 0);
+		gr_maybe_create_shader(SDR_TYPE_SHADOW_MAP_GEN, gr_is_capable(gr_capability::CAPABILITY_FAST_SHADOWS) ? 0 : SDR_FLAG_SHADOW_FALLBACK);
 
 	gr_maybe_create_shader(SDR_TYPE_MODEL, 0);