Don't add null characters to the end of the APFloat string buffer.

Report/patch inspiration by Olaf Krzikalla.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160744 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index 409d4fb..9f5ca3e 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -3278,16 +3278,8 @@
 }
 
 namespace {
-  static void append(SmallVectorImpl<char> &Buffer,
-                     unsigned N, const char *Str) {
-    unsigned Start = Buffer.size();
-    Buffer.set_size(Start + N);
-    memcpy(&Buffer[Start], Str, N);
-  }
-
-  template <unsigned N>
-  void append(SmallVectorImpl<char> &Buffer, const char (&Str)[N]) {
-    append(Buffer, N, Str);
+  void append(SmallVectorImpl<char> &Buffer, StringRef Str) {
+    Buffer.append(Str.begin(), Str.end());
   }
 
   /// Removes data from the given significand until it is no more