Create Unifier test: Unify(double, TypeReference(struct (0 double))) …

…=> TypeReference(struct (0 double))

```
Expected: "STR"
But was:  "(union (real64 u1) (STR u0))"
```

src/UnitTests/Decompiler/Typing/UnifierTests.cs

@@ -531,6 +531,17 @@ public void UnifyTypeReferences()
             Assert.AreEqual("CHAR", un.Unify(t1, t2).ToString());
         }
 
+        [Test]
+        public void UnifyDoubleWithFieldAt0OffsetOfTypeReferenceToStruct()
+        {
+            var t1 = new TypeReference("STR", new StructureType
+            {
+                Fields = { { 0, PrimitiveType.Real64 } }
+            });
+            var t2 = PrimitiveType.Real64;
+            Assert.AreEqual("STR", un.Unify(t1, t2).ToString());
+        }
+
         [Test]
         public void Unify_AreUnknownCompatible()
         {