Warning mismatch #if / #endif from preprocessor

When an included file is not terminated by means of a `\n` it is possible that we get a warning like:
```
warning: More #if's than #endif's found (might be in an included file).
```
adding the `\n`, as already done with files that are "normally" preprocessed , solves the problem

Author: albert-github

src/pre.l

@@ -2259,6 +2259,7 @@ static std::unique_ptr<FileState> checkAndOpenFile(yyscan_t yyscanner,const QCSt
     }
     else
     {
+      addTerminalCharIfMissing(fs->fileBuf,'\n');
       fs->oldFileBuf    = state->inputBuf;
       fs->oldFileBufPos = state->inputBufPos;
     }