An implicit style located in merged resource dictionary is not applied to the first control of the target type if the main resource dictionary is empty

* .NET Core Version: 3.0
* Windows version: Version 1903
* Does the bug reproduce also in WPF for .NET Framework 4.8?: Yes

**Problem description:**
Hello,

Please try the following setup:

```

<Setter Property="Text" Value="Test" />

```

**Actual behavior:**
The first TextBlock there does not have its Text set to "Test". If I uncomment the DummyString resource it works as expected.

**Expected behavior:**
The first TextBlock there has its Text set to "Test".

**Minimal repro:**
See https://github.com/Proxaaa/MergeTest/tree/master