luci-app-ssr-plus: update.lua: Fix path configuration failure caused by whitespace characters in special cases.

Fixed: https://github.com/fw876/helloworld/commit/c82145f45e34bba827e71cee7ac3ad0bc2732a95

经测试，本人遇到的特殊情况是指新固件升级后（概率问题），在ssrp正常运行再手动更新gfw数据库时，系统日志中出现无法找到dnsmasq.cfg01411c*目录的报错而导致gfw数据库文件拷贝失败，再次手动更新后却又正常。本pr已修复此问题。

luci-app-ssr-plus/root/usr/share/shadowsocksr/update.lua

@@ -10,15 +10,40 @@ local icount = 0
 local args = arg[1]
 local uci = luci.model.uci.cursor()
 
--- 以下设置更新数据库至 DNSMASQ 路径
--- 获取 DEFAULT_DNSMASQ_CFGID
+-- 以下设置更新数据库至 DNSMASQ 配置路径
+-- 获取 DNSMasq 配置 ID
 local DEFAULT_DNSMASQ_CFGID = uci:get_first("dhcp", "dnsmasq", ".name")
+
+if not DEFAULT_DNSMASQ_CFGID then
+    error("未找到默认的 DNSMasq 配置 ID")
+end
+
 -- 查找包含 conf-dir 选项的 dnsmasq.conf 文件路径
-local DNSMASQ_CONF_PATH = string.format("grep -l '^conf-dir=' /tmp/etc/dnsmasq.conf.%s*", DEFAULT_DNSMASQ_CFGID):gsub("%s+", "") -- 去除空白字符
--- 获取 DNSMASQ_CONF_DIR
-local DNSMASQ_CONF_DIR = string.format("grep '^conf-dir=' %s | cut -d'=' -f2 | head -n 1", DNSMASQ_CONF_PATH):gsub("%s+", "") -- 去除空白字符
--- 设置 TMP_DNSMASQ_PATH 路径
-local TMP_DNSMASQ_PATH = DNSMASQ_CONF_DIR .. "/dnsmasq-ssrplus.d"
+local DNSMASQ_CONF_PATH_CMD = string.format("grep -l '^conf-dir=' /tmp/etc/dnsmasq.conf.%s*", DEFAULT_DNSMASQ_CFGID)
+local DNSMASQ_CONF_PATH = io.popen(DNSMASQ_CONF_PATH_CMD):read("*l")
+
+if not DNSMASQ_CONF_PATH or DNSMASQ_CONF_PATH:match("^%s*$") then
+    error("无法找到包含 conf-dir 选项的 dnsmasq.conf 文件路径")
+end
+
+DNSMASQ_CONF_PATH = DNSMASQ_CONF_PATH:gsub("%s+", "") -- 去除空白字符
+
+-- 获取 DNSMASQ 配置路径
+local DNSMASQ_CONF_DIR_CMD = string.format("grep '^conf-dir=' %s | cut -d'=' -f2 | head -n 1", DNSMASQ_CONF_PATH)
+local DNSMASQ_CONF_DIR = io.popen(DNSMASQ_CONF_DIR_CMD):read("*l")
+
+if not DNSMASQ_CONF_DIR or DNSMASQ_CONF_DIR:match("^%s*$") then
+    error("无法提取 conf-dir 配置，请检查 dnsmasq.conf 文件内容")
+end
+
+DNSMASQ_CONF_DIR = DNSMASQ_CONF_DIR:gsub("%s+", "") -- 去除空白字符
+
+-- 设置 dnsmasq-ssrplus.d 目录路径，并去除路径末尾的斜杠
+local TMP_DNSMASQ_PATH = DNSMASQ_CONF_DIR:match("^(.-)/?$") .. "/dnsmasq-ssrplus.d"
+
+if not TMP_DNSMASQ_PATH or TMP_DNSMASQ_PATH:match("^%s*$") then
+    error("无法找到包含 dnsmasq 选项的 dnsmasq-ssrplus.d 目录路径")
+end
 
 local TMP_PATH = "/var/etc/ssrplus"
 -- match comments/title/whitelist/ip address/excluded_domain