Fix memleak in hp2ps

Issue discovered by Coverity scan, CID 43167.

Signed-off-by: Austin Seipp <austin@well-typed.com>

utils/hp2ps/HpFile.c

@@ -423,6 +423,8 @@ GetString(FILE *infp)
     stringbuffer[i] = '\0'; 
     thestring = copystring(stringbuffer);
 
+    free(stringbuffer);
+
     ASSERT(ch == '\"');
 
     ch = getc(infp);      /* skip the '\"' that terminates the string */