Add regression test

tests/cases/compiler/strictNullLogicalAndOr.ts

@@ -0,0 +1,15 @@
+// @strictNullChecks: true
+
+// Repro from #9113
+
+let sinOrCos = Math.random() < .5;
+let choice = sinOrCos && Math.sin || Math.cos;
+
+choice(Math.PI);
+
+function sq(n?: number): number {
+  const r = n !== undefined && n*n || 0;
+  return r;
+}
+
+sq(3);