Fix wrong test: boolean variable is never negative

This has been spotted by clang++.

src/Server.cpp

@@ -878,7 +878,7 @@ void LyXComm::endPipe(int & fd, string const & filename, bool write)
 		       << '\n' << strerror(errno) << endl;
 	}
 
-	if (FileName(filename).removeFile() < 0) {
+	if (!FileName(filename).removeFile()) {
 		lyxerr << "LyXComm: Could not remove pipe " << filename
 		       << '\n' << strerror(errno) << endl;
 	}

status.21x

@@ -70,7 +70,7 @@ What's new
 
 - Fix export of documents that use the LaTeX-packages mhchem and wasysym
   (bug 9266).
-  
+
 - Remove unnecessary preamble code in LaTeX export
   of documents using the class REVTeX 4.1 file (bug 4625).
 
@@ -96,6 +96,7 @@ What's new
 
 * INTERNALS
 
+- Fix wrong test in LyX server.
 
 
 * DOCUMENTATION AND LOCALIZATION