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/mycurve.cc

@@ -21,7 +21,7 @@
 #include <cstring>
 #include <gdkmm/types.h>
 
-MyCurve::MyCurve () : pipetteR(-1.f), pipetteG(-1.f), pipetteB(-1.f), pipetteVal(-1.f), listener(NULL), cursor_type( CSArrow)
+MyCurve::MyCurve () : pipetteR(-1.f), pipetteG(-1.f), pipetteB(-1.f), pipetteVal(-1.f), listener(nullptr), cursor_type( CSArrow)
 {
 
     graphX = get_allocation().get_width() - RADIUS * 2;
@@ -30,9 +30,9 @@ MyCurve::MyCurve () : pipetteR(-1.f), pipetteG(-1.f), pipetteB(-1.f), pipetteVal
     prevGraphH = graphH;
     buttonPressed = false;
     snapTo = ST_None;
-    leftBar = NULL;
-    bottomBar = NULL;
-    colorProvider = NULL;
+    leftBar = nullptr;
+    bottomBar = nullptr;
+    colorProvider = nullptr;
     sized = RS_Pending;
     snapToElmt = -100;
     curveIsDirty = true;
@@ -152,11 +152,11 @@ void MyCurve::on_style_changed (const Glib::RefPtr<Gtk::Style>& style)
 
 void MyCurve::refresh()
 {
-    if (leftBar != NULL) {
+    if (leftBar != nullptr) {
         leftBar->setDirty(true);
     }
 
-    if (bottomBar != NULL) {
+    if (bottomBar != nullptr) {
         bottomBar->setDirty(true);
     }