allow open_port with env vars with trailing '=' on Windows

Same problem that Steve Vinoski fixed for Unix. Similar fix done in
erts/emulator/sys/win32/sys_env.c for Windows.

Copy-paste from his commit-message:

The erlang:open_port spawn and spawn_executable directives can include
    an {env, Env} directive to set up environment variables for the
    spawned process. A bug in ert/emulator/sys/unix/sys.c prevented
    applications from using {env, Env} to set an environment variable
    whose value ended with a '=' (equal sign) character; the code mistook
    the trailing equal sign as an indication that an environment variable
    was to be cleared from the environment of the spawned process.

    For example, passing an {env, Env} of

    {env, [{"foo", "bar="}]}

    would result in the code in sys.c seeing a string of the form

    "foo=bar="

    The code would see the final '=' character and assume the directive
    wanted to clear a variable named "foo=bar" from the environment of the
    spawned process, rather than seeing it as a directive to set the
    environment variable "foo" to the value "bar=".

1 files changed, 4 insertions, 2 deletions

diff --git a/erts/emulator/sys/win32/sys_env.c b/erts/emulator/sys/win32/sys_env.c
index ac4be3f316..ecfe4d5ba3 100644
--- a/erts/emulator/sys/win32/sys_env.c
+++ b/erts/emulator/sys/win32/sys_env.c
@@ -145,15 +145,17 @@ merge_environment(char *old, char *add)
     for(j = 0; a_arg[j] != NULL; ++j){
 	char **tmp;
 	char *current = a_arg[j];
+	char *eq_p = strchr(current,'=');
+	int unset = (eq_p!=NULL && eq_p[1]=='\0');
 
 	if ((tmp = find_arg(c_arg, current)) != NULL) {
-	    if (current[strlen(current)-1] != '=') {
+	    if (!unset) {
 		*tmp = current;
 	    } else {
 		*tmp = c_arg[--i];
 		c_arg[i] = NULL;
 	    }
-	} else if (current[strlen(current)-1] != '=') {
+	} else if (!unset) {
 	    c_arg[i++] = current;
 	    c_arg[i] = NULL;
 	}