Fix Prevent maxForks less than zero [ci fast]

Signed-off-by: Paolo Di Tommaso <paolo.ditommaso@gmail.com>

modules/nextflow/src/main/groovy/nextflow/processor/TaskProcessor.groovy

@@ -306,7 +306,7 @@ class TaskProcessor {
         this.config = config
         this.taskBody = taskBody
         this.name = name
-        this.maxForks = config.maxForks ? config.maxForks as int : 0
+        this.maxForks = config.maxForks && config.maxForks>0 ? config.maxForks as int : 0
         this.forksCount = maxForks ? new LongAdder() : null
         this.isFair0 = config.getFair()
     }