Merge pull request #132 from archivaldo/fronting

small fix to allow fronting

httplib.h

@@ -2066,17 +2066,19 @@ inline void Client::write_request(Stream& strm, Request& req)
         path.c_str());
 
     // Headers
-    if (is_ssl()) {
-        if (port_ == 443) {
-            req.set_header("Host", host_.c_str());
-        } else {
-            req.set_header("Host", host_and_port_.c_str());
-        }
-    } else {
-        if (port_ == 80) {
-            req.set_header("Host", host_.c_str());
-        } else {
-            req.set_header("Host", host_and_port_.c_str());
+    if (!req.has_header("Host")) {
+        if (is_ssl()) {
+            if (port_ == 443) {
+				req.set_header("Host", host_.c_str());
+            } else {
+				req.set_header("Host", host_and_port_.c_str());
+			}
+		} else {
+			if (port_ == 80) {
+				req.set_header("Host", host_.c_str());
+			} else {
+				req.set_header("Host", host_and_port_.c_str());
+			}
         }
     }