Deal with zero sized ranges in Uniform correctly.

Change-Id: I6d5c622869e4795c252fa5c26fffbe4844abc3c9

internal/ceres/random.h

diff --git a/internal/ceres/random.h b/internal/ceres/random.h
index 2a02560..87d9d77 100644
--- a/internal/ceres/random.h
+++ b/internal/ceres/random.h
@@ -43,7 +43,11 @@
 }
 
 inline int Uniform(int n) {
-  return rand() % n;
+  if (n) {
+    return rand() % n;
+  } else {
+    return 0;
+  }
 }
 
 inline double RandDouble() {