clang-format: Fix error return when using inplace with stdin

[woodruffw]

Summary

Causes clang-format to exit with an appropriate error code
when the invalid combination of -i and stdin is provided.

[thakis]

Can you add a lit test for this?

[woodruffw]

Yep, I'll add one in a bit.

[thakis]

(marking this "request changes" to get it off my dashboard. please ping if you do add a test :) )

tools/clang-format/ClangFormat.cpp

for (const auto &R : Replaces) {
     outs() << "</replacement>\n";
   }
 }
 
 // Returns true on error.
 static bool format(StringRef FileName) {
   if (!OutputXML && Inplace && FileName == "-") {
     errs() << "error: cannot use -i when reading from stdin.\n";
-    return false;
+    return true;
   }
   // On Windows, overwriting a file with an open file mapping doesn't work,
   // so read the whole file into memory when formatting in-place.
   ErrorOr<std::unique_ptr<MemoryBuffer>> CodeOrErr =
       !OutputXML && Inplace ? MemoryBuffer::getFileAsStream(FileName) :
                               MemoryBuffer::getFileOrSTDIN(FileName);
   if (std::error_code EC = CodeOrErr.getError()) {
     errs() << EC.message() << "\n";