fix: do not panic on an invalid image name regexp

IsImageMatched interpolates the image name from kustomization images[].name
straight into a regexp and discarded the compile error. When the name is not
a valid regexp (for example "["), regexp.Compile returns a nil *Regexp and
the following MatchString call dereferences it, so kustomize build crashes with
a SIGSEGV.

Capture the compile error and return false when it is set. A name that can't
compile matches no image, which leaves the resource untouched (the same result
you get for any name that doesn't match). Adds a unit test for the invalid name
and a krusty end-to-end case that builds without panicking.

Signed-off-by: Arpit Jain <arpitjain099@gmail.com>

api/krusty/transformersimage_test.go

@@ -401,3 +401,42 @@ spec:
             image: solsa-echo:foo
 `)
 }
+
+// An images[].name value that is not a valid regexp (here "[") used to crash
+// the build with a nil-pointer panic. It should be treated as matching no
+// container image, so the resource passes through untouched.
+func TestTransfomersImageInvalidNameRegexp(t *testing.T) {
+	th := kusttest_test.MakeHarness(t)
+	th.WriteK(".", `
+resources:
+- deploy.yaml
+images:
+- name: "["
+  newTag: v2
+`)
+	th.WriteF("deploy.yaml", `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: deploy
+spec:
+  template:
+    spec:
+      containers:
+      - name: nginx
+        image: nginx:1.7.9
+`)
+	m := th.Run(".", th.MakeDefaultOptions())
+	th.AssertActualEqualsExpected(m, `
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: deploy
+spec:
+  template:
+    spec:
+      containers:
+      - image: nginx:1.7.9
+        name: nginx
+`)
+}