Apply modernize-use-nullptr

Setup:
- `mkdir tidy; cd tidy`
- `cmake .. -DCMAKE_BUILD_TYPE=debug -DPROC_TARGET_NUMBER=1 -DCACHE_NAME_SUFFIX=4 -DBINDIR=. -DDATADIR=. -DBUILD_BUNDLE=ON -DWITH_LTO=OFF -DOPTION_OMP=OFF -DCMAKE_EXPORT_COMPILE_COMMANDS=ON`
- `cd ..`
- `find -name '*.cc' -exec clang-tidy-3.8 -header-filter=.* -p=tidy -fix-errors -checks=modernize-use-nullptr {} \;`

rtgui/exifpanel.cc

@@ -25,7 +25,7 @@ using namespace rtengine;
 using namespace rtengine::procparams;
 using namespace rtexif;
 
-ExifPanel::ExifPanel () : idata(NULL)
+ExifPanel::ExifPanel () : idata(nullptr)
 {
 
     recursiveOp = true;
@@ -156,7 +156,7 @@ void ExifPanel::setImageData (const ImageMetaData* id)
     idata = id;
     exifTreeModel->clear ();
 
-    const std::vector<Tag*> defTags = ExifManager::getDefaultTIFFTags (NULL);
+    const std::vector<Tag*> defTags = ExifManager::getDefaultTIFFTags (nullptr);
 
     for (size_t i = 0; i < defTags.size(); i++) {
         Tag* defTag = defTags[i];