patch 8.1.1312: Coverity warning for using uninitialized variable

Problem:    Coverity warning for using uninitialized variable.
Solution:   Clear exarg_T.
diff --git a/src/quickfix.c b/src/quickfix.c
index 6157650..cf3b274 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -5809,6 +5809,7 @@
     {
 	exarg_T ea;
 
+	vim_memset(&ea, 0, sizeof(ea));
 	ea.arg = target_dir;
 	ea.cmdidx = CMD_lcd;
 	ex_cd(&ea);
@@ -6109,6 +6110,7 @@
 	    // appropriate ex command and executing it.
 	    exarg_T ea;
 
+	    vim_memset(&ea, 0, sizeof(ea));
 	    ea.arg = dirname_start;
 	    ea.cmdidx = (curwin->w_localdir == NULL) ? CMD_cd : CMD_lcd;
 	    ex_cd(&ea);