TemporaryBuffer: Fix reading from in-memory InputStream

I had the conditions wrong here, causing the in-memory InputStream
to always appear to be at EOF.

Change-Id: I6811d6187a34eaf1fd6c5002550d631decdfc391
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit.test/tst/org/eclipse/jgit/util/TemporaryBufferTest.java

@@ -52,6 +52,7 @@ import static org.junit.Assert.fail;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.Arrays;
 
 import org.eclipse.jgit.junit.TestRng;
@@ -248,6 +249,20 @@ public class TemporaryBufferTest {
 		}
 	}
 
+	@Test
+	public void testInCoreInputStream() throws IOException {
+		final int cnt = 256;
+		final byte[] test = new TestRng(getName()).nextBytes(cnt);
+		final TemporaryBuffer.Heap b = new TemporaryBuffer.Heap(cnt + 4);
+		b.write(test);
+		b.close();
+
+		InputStream in = b.openInputStream();
+		byte[] act = new byte[cnt];
+		IO.readFully(in, act, 0, cnt);
+		assertTrue(Arrays.equals(test, act));
+	}
+
 	@Test
 	public void testInCoreLimit_SwitchOnAppendByte() throws IOException {
 		final TemporaryBuffer b = new TemporaryBuffer.LocalFile();

org.eclipse.jgit/src/org/eclipse/jgit/util/TemporaryBuffer.java

@@ -548,7 +548,7 @@ public abstract class TemporaryBuffer extends OutputStream {
 			long skipped = 0;
 			while (0 < cnt) {
 				int n = (int) Math.min(block.count - blockPos, cnt);
-				if (n < 0) {
+				if (0 < n) {
 					blockPos += n;
 					skipped += n;
 					cnt -= n;
@@ -567,11 +567,12 @@ public abstract class TemporaryBuffer extends OutputStream {
 			int copied = 0;
 			while (0 < len) {
 				int c = Math.min(block.count - blockPos, len);
-				if (c < 0) {
+				if (0 < c) {
 					System.arraycopy(block.buffer, blockPos, b, off, c);
 					blockPos += c;
 					off += c;
 					len -= c;
+					copied += c;
 				} else if (nextBlock())
 					continue;
 				else