Fixed bug in __independent_bits_engine found by Nick (from stackoverflow)

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@143104 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/algorithm b/include/algorithm
index e662632..a89b9dd 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -2548,7 +2548,7 @@
         {
             __u = __e_() - _Engine::min();
         } while (__u >= __y0_);
-        if (__w0_ < _EDt)
+        if (__w0_ < _WDt)
             _S <<= __w0_;
         else
             _S = 0;
@@ -2561,7 +2561,7 @@
         {
             __u = __e_() - _Engine::min();
         } while (__u >= __y1_);
-        if (__w0_ < _EDt - 1)
+        if (__w0_ < _WDt - 1)
             _S <<= __w0_ + 1;
         else
             _S = 0;