Drop user from db that doesn't exist

[aldor007]

{"level":"error","ts":1633984857.1020865,"logger":"controller-runtime.manager.controller.mariadbdatabase","msg":"Reconciler error","reconciler group":"mariadb.mkaciuba.com","reconciler kind":"MariaDBDatabase","name":"mariadbdatabase-sample","namespace":"default","error":"MariaDBCluster.mariadb.mkaciuba.com "cluster-sample" not found","stacktrace":"github.com/go-logr/zapr.(*zapLogger).Error\n\t/go/pkg/mod/github.com/go-logr/zapr@v0.2.0/zapr.go:132\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.8.3/pkg/internal/controller/controller.go:302\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.8.3/pkg/internal/controller/controller.go:253\nsigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func1.2\n\t/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.8.3/pkg/internal/controller/controller.go:216\nk8s.io/apimachinery/pkg/util/wait.JitterUntilWithContext.func1\n\t/go/pkg/mod/k8s.io/apimachinery@v0.20.4/pkg/util/wait/wait.go:185\nk8s.io/apimachinery/pkg/util/wait.BackoffUntil.func1\n\t/go/pkg/mod/k8s.io/apimachinery@v0.20.4/pkg/util/wait/wait.go:155\nk8s.io/apimachinery/pkg/util/wait.BackoffUntil\n\t/go/pkg/mod/k8s.io/apimachinery@v0.20.4/pkg/util/wait/wait.go:156\nk8s.io/apimachinery/pkg/util/wait.JitterUntil\n\t/go/pkg/mod/k8s.io/apimachinery@v0.20.4/pkg/util/wait/wait.go:133\nk8s.io/apimachinery/pkg/util/wait.JitterUntilWithContext\n\t/go/pkg/mod/k8s.io/apimachinery@v0.20.4/pkg/util/wait/wait.go:185\nk8s.io/apimachinery/pkg/util/wait.UntilWithContext\n\t/go/pkg/mod/k8s.io/apimachinery@v0.20.4/pkg/util/wait/wait.go:99"}
E1011 20:40:57.117076 1 runtime.go:78] Observed a panic: "invalid memory address or nil pointer dereference" (runtime error: invalid memory address or nil pointer dereference)
goroutine 335 [running]:
k8s.io/apimachinery/pkg/util/runtime.logPanic(0x1002240, 0x1d682d0)
/go/pkg/mod/k8s.io/apimachinery@v0.20.4/pkg/util/runtime/runtime.go:74 +0x84
k8s.io/apimachinery/pkg/util/runtime.HandleCrash(0x0, 0x0, 0x0)
/go/pkg/mod/k8s.io/apimachinery@v0.20.4/pkg/util/runtime/runtime.go:48 +0x7c
panic(0x1002240, 0x1d682d0)
/usr/local/go/src/runtime/panic.go:969 +0x15c
github.com/aldor007/mariadb-operator/contro