NPE on Azure Machine Creations

[prashanth26]

Issue

@rfranzke observed NPEs while trying to create machines which didn't have an AzureMachineClass backing it. He mentioned that it might be related to quota issues? Need to further investigate.

Logs

I0223 09:36:13.048282       1 machine_util.go:109] AzureMachineClass "shoot--vlabaz0006--ibgubkxfiq-worker-f7fie-26bde" not found. Skipping. azuremachineclass.machine.sapcloud.io "shoot--vlabaz0006--ibgubkxfiq-worker-f7fie-26bde" not found
I0223 09:36:13.098536       1 machine.go:315] Creating machine shoot--vlabaz0006--ibgubkxfiq-worker-comxa-5c646bdf8d-zssnx, please wait!
E0223 09:36:13.348035       1 runtime.go:66] Observed a panic: "invalid memory address or nil pointer dereference" (runtime error: invalid memory address or nil pointer dereference)
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:72
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:65
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:51
/usr/local/go/src/runtime/asm_amd64.s:522
/usr/local/go/src/runtime/panic.go:513
/usr/local/go/src/runtime/panic.go:82
/usr/local/go/src/runtime/signal_unix.go:390
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/pkg/driver/driver_azure.go:80
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/pkg/controller/machine.go:317
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/pkg/controller/machine.go:184
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/pkg/controller/machine.go:108
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/pkg/controller/controller.go:492
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/pkg/controller/controller.go:534
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/pkg/controller/controller.go:551
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:133
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:134
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/vendor/k8s.io/apimachinery/pkg/util/wait/wait.go:88
/tmp/build/80754af9/git-gardener_machine-controller-manager-master_master/tmp/src/github.com/gardener/machine-controller-manager/pkg/controller/controller.go:513
/usr/local/go/src/runtime/asm_amd64.s:1333
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
    panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x16a126a]