unistd, sys.socket: fix unsigned ret type when ssize_t required.

Fixes #354, Fixes #361
* ext/posix/sys/socket.c (Precv): Don't try to put a negative result
into an unsigned variable.
* ext/posix/unistd.c (Pread): Likewise.
* NEWS.md (Bugs Fized): Updated.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>

NEWS.md

@@ -14,6 +14,10 @@
 
 ### Bugs Fixed
 
+  - `posix.unistd.read` and `posix.sys.socket.recv` no longer
+    hide the underlying real error by casting a ssize_t result
+    into an unsigned site_t local.
+
   - Fix a typo in the `lflag` argument name in the termios
     table LDocs.
 

ext/posix/sys/socket.c

@@ -536,7 +536,8 @@ static int
 Precv(lua_State *L)
 {
 	int fd = checkint(L, 1);
-	size_t count = (size_t)checkinteger(L, 2), ret;
+	size_t count = (size_t)checkinteger(L, 2);
+	ssize_t ret;
 	void *ud, *buf;
 	lua_Alloc lalloc;
 

ext/posix/unistd.c

@@ -930,7 +930,8 @@ static int
 Pread(lua_State *L)
 {
 	int fd = checkint(L, 1);
-	size_t count = (size_t)checkinteger(L, 2), ret;
+	size_t count = (size_t)checkinteger(L, 2);
+	ssize_t ret;
 	void *ud, *buf;
 	lua_Alloc lalloc;