Fixing source build script search, attempt to fix KT-8705

(cherry picked from commit 89c5885)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinPluginWrapper.kt

@@ -55,7 +55,7 @@ abstract class KotlinBasePluginWrapper: Plugin<Project> {
                 return scriptHandler
             }
             log.kotlinDebug("not found, switching to parent")
-            curProject = curProject.getParent()!!
+            curProject = curProject.getParent() ?: break
         }
         return null
     }