fix capacity in stringbuffers

rtl_stringbuffer_* functions silently allocate +16 extra for capacity,
but rtl_string_* functions do not. As intuitive and obvious as ever.

Change-Id: Ia0bb63dedf31f6ad5c687187221d7385043b5456

sal/inc/rtl/strbuf.hxx

@@ -229,11 +229,12 @@ public:
     {
         const int l = c.length();
         rtl_String* buffer = NULL;
-        rtl_string_new_WithLength( &buffer, l );
+        nCapacity = l + 16;
+        rtl_string_new_WithLength( &buffer, nCapacity );
         char* end = c.addData( buffer->buffer );
+        *end = '\0';
         buffer->length = end - buffer->buffer;
         pData = buffer;
-        nCapacity = l + 16;
     }
 #endif
 

sal/inc/rtl/ustrbuf.hxx

@@ -221,12 +221,13 @@ public:
     {
         const int l = c.length();
         rtl_uString* buffer = NULL;
-        rtl_uString_new_WithLength( &buffer, l ); // TODO this clears, not necessary
+        nCapacity = l + 16;
+        rtl_uString_new_WithLength( &buffer, nCapacity ); // TODO this clears, not necessary
         sal_Unicode* end = c.addData( buffer->buffer );
+        *end = '\0';
         buffer->length = end - buffer->buffer;
         // TODO realloc in case buffer->length is noticeably smaller than l ?
         pData = buffer;
-        nCapacity = l + 16;
     }
 #endif
     /** Assign to this a copy of value.