gpu/internal/vulkan: resize descriptor set pool correctly

Before this change, the resized descriptor set pool would never
increase, defeating the purpose of re-using pools.

References: https://todo.sr.ht/~eliasnaur/gio/375
Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/internal/vulkan/vulkan.go

@@ -691,9 +691,9 @@ func (p *descPool) bindDescriptorSet(b *Backend, cmdBuf vk.CommandBuffer, bindPo
 			if realloced {
 				panic("vulkan: vkAllocateDescriptorSet failed on a newly allocated descriptor pool")
 			}
+			newCap := p.cap * 2
 			destroyPool()
 			realloced = true
-			newCap := p.cap * 2
 			const initialPoolSize = 100
 			if newCap < initialPoolSize {
 				newCap = initialPoolSize