[ fixed #242 ] segfault due to buffer overrun in C++ printer

After some buffer resizings, trying to strcpy the buffer into a buffer
of the initial size will fail spectacularly.  Exposed on Mac OS X.

The copying was anyway silly if the buffer is to be filled with zeros
afterwards, thus, simply don't do it!

source/src/BNFC/Backend/CPP/PrettyPrinter.hs

@@ -137,10 +137,15 @@ mkHFile useStl inPackage cf groups = unlines
     if useStl then render (nest 2 bufAppendString) else "",
     "  void inline bufReset(void)",
     "  {",
-    "    cur_ = 0;",
+    "    if (buf_) free(buf_);",
     "    buf_size = " ++ nsDefine inPackage "BUFFER_INITIAL" ++ ";",
-    "    resizeBuffer();",
+    "    buf_ = (char *) malloc(buf_size);",
+    "    if (!buf_) {",
+    "      fprintf(stderr, \"Error: Out of memory while allocating buffer!\\n\");",
+    "      exit(1);",
+    "    }",
     "    memset(buf_, 0, buf_size);",
+    "    cur_ = 0;",
     "  }",
     "",
     "  void inline resizeBuffer(void)",