fstream.tcc (xsgetn): Slightly tweak the recent fix for 11722...

2004-09-14  Nathan Myers  <ncm@cantrip.org>

	* include/bits/fstream.tcc (xsgetn): Slightly tweak the recent fix
	for 11722: copy can replace move; the common case is __avail == 0.

From-SVN: r87501

libstdc++-v3/ChangeLog

+2004-09-14  Nathan Myers  <ncm@cantrip.org>
+
+	* include/bits/fstream.tcc (xsgetn): Slightly tweak the recent fix
+	for 11722: copy can replace move; the common case is __avail == 0.
+
 2004-09-14  Paolo Carlini  <pcarlini@suse.de>
 
 	* include/bits/cpp_type_traits.h: Rename __is_trivially_copyable

libstdc++-v3/include/bits/fstream.tcc

@@ -524,14 +524,17 @@ namespace std
 	 {
 	   // First, copy the chars already present in the buffer.
 	   const streamsize __avail = this->egptr() - this->gptr();
-	   if (__avail == 1)
-	     *__s = *this->gptr();
-	   else if (__avail > 1)
-	     traits_type::move(__s, this->gptr(), __avail);
-	   __s += __avail;
-	   this->gbump(__avail);
-	   __ret += __avail;
-	   __n -= __avail;
+	   if (__avail != 0)
+	     {
+	       if (__avail == 1)
+		 *__s = *this->gptr();
+	       else if (__avail > 1)
+		 traits_type::copy(__s, this->gptr(), __avail);
+	       __s += __avail;
+	       this->gbump(__avail);
+	       __ret += __avail;
+	       __n -= __avail;
+	     }
 
 	   const streamsize __len = _M_file.xsgetn(reinterpret_cast<char*>(__s),
 						   __n);