grabber: remove direct link between panel offset and mouse coordinate delta

feedlist.js

@@ -488,6 +488,10 @@ function mouse_move_handler(e) {
 			if (mouse_x == 0) mouse_x = client_x;
 
 			resize_headlines(mouse_x - client_x, mouse_y - client_y);
+
+			mouse_y = client_y;
+			mouse_x = client_x;
+
 			return false;
 		}
 
@@ -502,7 +506,11 @@ function resize_enabled(b) {
 
 function mouse_down_handler(e) {
 	try {
-		if (enable_resize) mouse_is_down = true;
+		if (enable_resize) { 
+			mouse_is_down = true;
+			mouse_x = 0;
+			mouse_y = 0;
+		}
 	} catch (e) {
 		exception_error("mouse_move_handler", e);
 	}

tt-rss.js

@@ -377,7 +377,7 @@ function resize_headlines(delta_x, delta_y) {
 
 		if (c_frame.offsetLeft > feeds_frame.offsetWidth + feeds_frame.offsetLeft + 100) {
 			if (delta_x != undefined) {
-				hor_offset = delta_x;
+				hor_offset = hor_offset + delta_x;
 			}
 		}
 
@@ -394,7 +394,7 @@ function resize_headlines(delta_x, delta_y) {
 	} else {
 
 		if (delta_y != undefined) {
-			ver_offset = delta_y;
+			ver_offset = ver_offset + delta_y;
 		}
 
 		debug("resize_headlines: VER-mode");