Ensure termination in case of incorrect usage.

src/pio_client.c

@@ -79,7 +79,7 @@ cdiPioClientStreamOpen(const char *filename, char filemode,
         }
     }
   else
-    Error("cdiPIO read support not implemented");
+    xabort("cdiPIO read support not implemented");
   return fileID;
 }