dx incorrectly writes registers as a signed leb128 in the dex debug info

This has no functional effect, because reading the signed leb128 value
as an unsignedleb128 still produces the same value. But the encoding is
1 byte longer in some cases.
diff --git a/dx/src/com/android/dx/dex/file/DebugInfoEncoder.java b/dx/src/com/android/dx/dex/file/DebugInfoEncoder.java
index 780e18d..3d36aed 100644
--- a/dx/src/com/android/dx/dex/file/DebugInfoEncoder.java
+++ b/dx/src/com/android/dx/dex/file/DebugInfoEncoder.java
@@ -901,7 +901,7 @@
                     "Signed value where unsigned required: " + n);
         }
 
-        output.writeSignedLeb128(n);
+        output.writeUnsignedLeb128(n);
     }
 
     /**