Throw exception when base.InitializeTarget() is not called + inline GetAllLayouts()

[304NotModified]

• Target.GetAllLayouts() was useless a method (once called, private). So inlined it.
• If you write a target and forgot to call base.InitializeTarget(), you can get a nullRefException in Target.PrecalculateVolatileLayouts (called in AsyncWrapper/BufferWrapper). The nullref is now fixed, but you still get odd behaviour, so we will check ifbase.InitializeTarget()` has been called.

[codecov-io]

Current coverage is 74.03%

Merging #1191 into master will increase coverage by +0.03% as of 145b1f8

@@            master   #1191   diff @@
======================================
  Files          265     265       
  Stmts        15296   15299     +3
  Branches      1679    1681     +2
  Methods          0       0       
======================================
+ Hit          11320   11326     +6
- Partial        417     419     +2
+ Missed        3559    3554     -5

Review entire Coverage Diff as of 145b1f8

---

Uncovered Suggestions

1. +0.08% via ...argets/FileTarget.cs#1722...1734
2. +0.07% via ...gingConfiguration.cs#282...293
3. +0.07% via ...gingConfiguration.cs#244...255
4. See 7 more...

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[bhaeussermann]

Whoops! It seems after merging the test now throws NLogRuntimeException instead of NLogConfigurationException. The original exception is no longer caught and rethrown as an NLogConfigurationException. This is probably fine as the exception does not occur due to a configuration error. What do you think?

[304NotModified]

Whoops! It seems after merging the test now throws NLogRuntimeException instead of NLogConfigurationException. The original exception is no longer caught and rethrown as an NLogConfigurationException. This is probably fine as the exception does not occur due to a configuration error. What do you think?

I think NLogRuntimeException is more suitable?

[304NotModified]

Changed to NLogRuntimeException is the unit test