don't reduce requested if already Long.MAX_VALUE

Author: davidmoten

src/main/java/rx/internal/operators/OnSubscribeRedo.java

@@ -500,10 +500,12 @@ void emit(long mreq, Producer mp, long mprod) {
             long u = requested + mreq;
             if (u < 0) {
                 u = Long.MAX_VALUE;
-            }
-            u -= mprod;
-            if (u < 0) {
-                throw new IllegalStateException("More produced than requested");
+            } else 
+            if (u != Long.MAX_VALUE) {
+                u -= mprod;
+                if (u < 0) {
+                    throw new IllegalStateException("More produced than requested");
+                }
             }
             requested = u;