Fix some example C++ Warnings

Author: RobLoach

examples/core/core_drop_files.cpp

@@ -48,7 +48,7 @@ int main() {
                 raylib::DrawText("Dropped files:", 100, 40, 20, DARKGRAY);
 
                 // Iterate through all the dropped files.
-                for (int i = 0; i < droppedFiles.size(); i++) {
+                for (int i = 0; i < (int)droppedFiles.size(); i++) {
                     if (i % 2 == 0)
                         DrawRectangle(0, 85 + 40*i, screenWidth, 40, Fade(LIGHTGRAY, 0.5f));
                     else

examples/core/core_loading_thread.cpp

@@ -55,7 +55,7 @@ int main(void)
                         threadId = std::thread(LoadDataThread);
                         TraceLog(LOG_INFO,
                             "Loading thread initialized successfully");
-                    } catch (std::system_error e) {
+                    } catch (std::system_error& e) {
                         TraceLog(LOG_ERROR, "Error: %s", e.what());
                     }
 

examples/core/core_window_letterbox.cpp

@@ -41,7 +41,7 @@ int main(void)
     raylib::RenderTexture2D target(gameScreenWidth, gameScreenHeight);
     target.GetTexture().SetFilter(TEXTURE_FILTER_BILINEAR); // Texture scale filter to use
 
-    raylib::Color colors[10] = { 0 };
+    raylib::Color colors[10];
     for (int i = 0; i < 10; i++) {
         colors[i] = raylib::Color((unsigned char)GetRandomValue(100, 250), (unsigned char)GetRandomValue(50, 150), (unsigned char)GetRandomValue(10, 100), 255);
     }
@@ -60,7 +60,9 @@ int main(void)
         if (IsKeyPressed(KEY_SPACE))
         {
             // Recalculate random colors for the bars
-            for (int i = 0; i < 10; i++) colors[i] = (Color){ (unsigned char)GetRandomValue(100, 250), (unsigned char)GetRandomValue(50, 150), (unsigned char)GetRandomValue(10, 100), 255 };
+            for (int i = 0; i < 10; i++) {
+                colors[i] = raylib::Color((unsigned char)GetRandomValue(100, 250), (unsigned char)GetRandomValue(50, 150), (unsigned char)GetRandomValue(10, 100), 255);
+            }
         }
 
         // Update virtual mouse (clamped mouse value behind game screen)