internal/graphicscommand: add a debug.IsDebug check before splitting …

…strings (#3134)

Since `debug.IsDebug` is a constant, by putting the `strings.Cut` calls inside the check this makes the
`(*commandqueue).flush` method faster when Ebitengine is compiled without the debug build tag.

Without the if `debug.IsDebug` check, unnecessary allocations occur (since the logger is a noop logger when debug is
disabled).

internal/graphicscommand/commandqueue.go

@@ -305,14 +305,16 @@ func (q *commandQueue) flush(graphicsDriver graphicsdriver.Graphics, endFrame bo
 			if err := c.Exec(q, graphicsDriver, indexOffset); err != nil {
 				return err
 			}
-			str := c.String()
-			for {
-				head, tail, ok := strings.Cut(str, "\n")
-				logger.FrameLogf("  %s\n", head)
-				if !ok {
-					break
+			if debug.IsDebug {
+				str := c.String()
+				for {
+					head, tail, ok := strings.Cut(str, "\n")
+					logger.FrameLogf("  %s\n", head)
+					if !ok {
+						break
+					}
+					str = tail
 				}
-				str = tail
 			}
 			// TODO: indexOffset should be reset if the command type is different
 			// from the previous one. This fix is needed when another drawing command is