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 {} \;`

rtengine/alignedbuffer.h

@@ -43,7 +43,7 @@ public:
     * @param size Number of elements of size T to allocate, i.e. allocated size will be sizeof(T)*size ; set it to 0 if you want to defer the allocation
     * @param align Expressed in bytes; SSE instructions need 128 bits alignment, which mean 16 bytes, which is the default value
     */
-    AlignedBuffer (size_t size = 0, size_t align = 16) : real(NULL), alignment(align), allocatedSize(0), unitSize(0), data(NULL), inUse(false)
+    AlignedBuffer (size_t size = 0, size_t align = 16) : real(nullptr), alignment(align), allocatedSize(0), unitSize(0), data(nullptr), inUse(false)
     {
         if (size) {
             resize(size);
@@ -78,8 +78,8 @@ public:
                     free(real);
                 }
 
-                real = NULL;
-                data = NULL;
+                real = nullptr;
+                data = nullptr;
                 inUse = false;
                 allocatedSize = 0;
                 unitSize = 0;
@@ -117,7 +117,7 @@ public:
                 } else {
                     allocatedSize = 0;
                     unitSize = 0;
-                    data = NULL;
+                    data = nullptr;
                     inUse = false;
                     return false;
                 }