gRPC: fixed possible sign extension of error and setting_value.

All cases are harmless and should not happen on valid values, though can
result in bad values being shown incorrectly in logs.

Found by Coverity (CID 1430311, 1430312, 1430313).

src/http/modules/ngx_http_grpc_module.c

diff --git a/src/http/modules/ngx_http_grpc_module.c b/src/http/modules/ngx_http_grpc_module.c
index b6be9b8..837ad9a 100644
--- a/src/http/modules/ngx_http_grpc_module.c
+++ b/src/http/modules/ngx_http_grpc_module.c
@@ -3212,7 +3212,7 @@
         switch (state) {
 
         case sw_start:
-            ctx->error = ch << 24;
+            ctx->error = (ngx_uint_t) ch << 24;
             state = sw_error_2;
             break;
 
@@ -3325,7 +3325,7 @@
             break;
 
         case sw_error:
-            ctx->error = ch << 24;
+            ctx->error = (ngx_uint_t) ch << 24;
             state = sw_error_2;
             break;
 
@@ -3555,7 +3555,7 @@
             break;
 
         case sw_value:
-            ctx->setting_value = ch << 24;
+            ctx->setting_value = (ngx_uint_t) ch << 24;
             state = sw_value_2;
             break;