bootmanager: Minor tidiness/correctness changes

Moved over from #3266 in citra.

src/yuzu/bootmanager.h

@@ -58,7 +58,7 @@ public:
      * @return True if the emulation thread is running, otherwise false
      * @note This function is thread-safe
      */
-    bool IsRunning() {
+    bool IsRunning() const {
         return running;
     }
 
@@ -68,12 +68,12 @@ public:
     void RequestStop() {
         stop_run = true;
         SetRunning(false);
-    };
+    }
 
 private:
-    bool exec_step;
-    bool running;
-    std::atomic<bool> stop_run;
+    bool exec_step = false;
+    bool running = false;
+    std::atomic<bool> stop_run{false};
     std::mutex running_mutex;
     std::condition_variable running_cv;