Make sure the output of sqlite3OsFullPathname is initialized even if the

fails due to I/O or OOM errors.

FossilOrigin-Name: e4943adb83819dee06e2e9da25ff6d967ca170de

src/os.c

@@ -138,6 +138,7 @@ int sqlite3OsFullPathname(
   int nPathOut, 
   char *zPathOut
 ){
+  zPathOut[0] = 0;
   return pVfs->xFullPathname(pVfs, zPath, nPathOut, zPathOut);
 }
 #ifndef SQLITE_OMIT_LOAD_EXTENSION