Fail if splitFastq receives incomplete record (#6268)

Signed-off-by: Ben Sherman <bentshermann@gmail.com>

Author: bentsherman

modules/nextflow/src/main/groovy/nextflow/splitter/FastqSplitter.groovy

@@ -134,14 +134,17 @@ class FastqSplitter extends AbstractTextSplitter {
     @Override
     protected fetchRecord(BufferedReader reader) {
 
-        def l1 = reader.readLine()
-        def l2 = reader.readLine()
-        def l3 = reader.readLine()
-        def l4 = reader.readLine()
+        final l1 = reader.readLine()
+        final l2 = reader.readLine()
+        final l3 = reader.readLine()
+        final l4 = reader.readLine()
 
-        if( !l1 || !l2 || !l3 || !l4 )
+        if( !l1 && !l2 && !l3 && !l4 )
             return null
 
+        if( !l1 || !l2 || !l3 || !l4 )
+            throw new IllegalStateException(errorMessage)
+
         if( !l1.startsWith('@') || !l3.startsWith('+') )
             throw new IllegalStateException(errorMessage)