Merge pull request ReactiveX#1964 from zsxwing/fix-buffer-request

Handle 0 or negative request in Buffer

Author: benjchristensen

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

@@ -144,6 +144,12 @@ private void requestInfinite() {
 
                     @Override
                     public void request(long n) {
+                        if (n == 0) {
+                            return;
+                        }
+                        if (n < 0) {
+                            throw new IllegalArgumentException("request a negative number: " + n);
+                        }
                         if (infinite) {
                             return;
                         }