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/clipboard.cc

@@ -41,7 +41,7 @@ void Clipboard::setPartialProfile   (const rtengine::procparams::PartialProfile&
     } else {
         if (partProfile.pparams) {
             delete partProfile.pparams;
-            partProfile.pparams = NULL;
+            partProfile.pparams = nullptr;
         }
     }
 
@@ -54,7 +54,7 @@ void Clipboard::setPartialProfile   (const rtengine::procparams::PartialProfile&
     } else {
         if (partProfile.pedited) {
             delete partProfile.pedited;
-            partProfile.pedited = NULL;
+            partProfile.pedited = nullptr;
         }
     }
 }
@@ -74,6 +74,6 @@ void Clipboard::setProcParams (const rtengine::procparams::ProcParams& pparams)
     // delete pedited
     if (partProfile.pedited) {
         delete partProfile.pedited;
-        partProfile.pedited = NULL;
+        partProfile.pedited = nullptr;
     }
 }