Fix using SDCV_PAGER

Stream opened with popen() should be closed with pclose() as documented
in popen(3) man.

src/libwrapper.cpp

@@ -288,7 +288,7 @@ namespace {
         sdcv_pager& operator=(const sdcv_pager&) = delete;
         ~sdcv_pager() {
             if (output != stdout)
-                fclose(output);
+                pclose(output);
         }
         FILE *get_stream() { return output; }
     private: