SLING-8660 - Add optional support for precompiled scripts in the HTL engine

* corrected RenderUnit lookup depending on the scenario (precompiled or source)
diff --git a/src/main/java/org/apache/sling/scripting/sightly/impl/engine/SightlyScriptEngine.java b/src/main/java/org/apache/sling/scripting/sightly/impl/engine/SightlyScriptEngine.java
index 5a15583..d11bdee 100644
--- a/src/main/java/org/apache/sling/scripting/sightly/impl/engine/SightlyScriptEngine.java
+++ b/src/main/java/org/apache/sling/scripting/sightly/impl/engine/SightlyScriptEngine.java
@@ -71,8 +71,7 @@
             SightlyCompiledScript compiledScript = null;
             if (precompiledUnitManager != null) {
                 compiledScript = precompiledUnitManager.evaluate(this, scriptContext);
-            }
-            if (slingHTLMasterCompiler != null) {
+            } else if (slingHTLMasterCompiler != null) {
                 compiledScript = slingHTLMasterCompiler.compileHTLScript(this, reader, scriptContext);
             }
             if (compiledScript != null) {