ParameterScriptProcessor: reset state upon begin

When we start processing a new ScriptInfo with the same instance,
let's reset the state so that everything works properly.

Author: ctrueden

src/main/java/org/scijava/script/process/ParameterScriptProcessor.java

@@ -119,14 +119,15 @@ public class ParameterScriptProcessor implements ScriptProcessor {
 	private LogService log;
 
 	private ScriptInfo info;
-	private boolean header = true;
+	private boolean header;
 
 	// -- ScriptProcessor methods --
 
 	@Override
 	public void begin(final ScriptInfo scriptInfo) {
 		info = scriptInfo;
 		info.setReturnValueAppended(true);
+		header = true;
 	}
 
 	@Override