core: Fix clang-tidy modernize-use-nullptr warnings

src/core/model/breakpoint.cc

@@ -52,17 +52,17 @@ BreakpointFallback()
 #else
 
 void
-BreakpointFallback(void)
+BreakpointFallback()
 {
     NS_LOG_FUNCTION_NOARGS();
 
-    int* a = 0;
+    int* a = nullptr;
     /**
      * we test here to allow a debugger to change the value of
      * the variable 'a' to allow the debugger to avoid the
      * subsequent segfault.
      */
-    if (a == 0)
+    if (a == nullptr)
     {
         *a = 0;
     }

src/core/model/system-path.cc

@@ -186,13 +186,13 @@ FindSelfDirectory()
         //  LPTSTR = char *
         DWORD size = 1024;
         LPTSTR lpFilename = (LPTSTR)malloc(sizeof(TCHAR) * size);
-        DWORD status = GetModuleFileName(0, lpFilename, size);
+        DWORD status = GetModuleFileName(nullptr, lpFilename, size);
         while (status == size)
         {
             size = size * 2;
             free(lpFilename);
             lpFilename = (LPTSTR)malloc(sizeof(TCHAR) * size);
-            status = GetModuleFileName(0, lpFilename, size);
+            status = GetModuleFileName(nullptr, lpFilename, size);
         }
         NS_ASSERT(status != 0);
         filename = lpFilename;