Improve FIFO analyzer search function

- Only one search result is generated per command/line, even if there are multiple matches in that line.
- Pressing enter on the edit field begins a search, just like clicking the begin button.
- The next and previous buttons are disabled until a search is begun.
- The search results are cleared when changing objects or frames.
- The previous button once again works (a regression from the previous commit), and the register updates and graphics data for the correct object are searched.
- currentRow() never returns -1, so checking that is unnecessary (and misleading).
- The 'Invalid search parameters (no object selected)' previously never showed up before because FRAME_ROLE is present if and only if OBJECT_ROLE is present.

Source/Core/DolphinQt/FIFO/FIFOAnalyzer.h

@@ -8,6 +8,8 @@
 
 #include <QWidget>
 
+#include "Common/CommonTypes.h"
+
 class QGroupBox;
 class QLabel;
 class QLineEdit;
@@ -57,9 +59,13 @@ private:
 
   struct SearchResult
   {
-    int frame;
-    int object;
-    int cmd;
+    constexpr SearchResult(u32 frame, u32 object, u32 cmd)
+        : m_frame(frame), m_object(object), m_cmd(cmd)
+    {
+    }
+    const u32 m_frame;
+    const u32 m_object;
+    const u32 m_cmd;
   };
 
   std::vector<int> m_object_data_offsets;