Fixed exec*(), and __flatten_process_args() with NULL env.

* Not sure if it's following any standard, but environ can be NULL
  (either by manually setting it to NULL, or by calling clearenv()).

src/system/libroot/os/image.cpp

@@ -412,6 +412,7 @@ __test_executable(const char *path, char *invoker)
 	into it. The buffer starts with a char* array which contains pointers to
 	the strings of the arguments and environment, followed by the strings. Both
 	arguments and environment arrays are NULL-terminated.
+
 	If executablePath is non-NULL, it should refer to the executable to be
 	executed. If the executable file specifies changes to environment variable
 	values, those will be performed.
@@ -421,7 +422,7 @@ __flatten_process_args(const char* const* args, int32 argCount,
 	const char* const* env, int32* _envCount, const char* executablePath,
 	char*** _flatArgs, size_t* _flatSize)
 {
-	if (args == NULL || env == NULL || _envCount == NULL)
+	if (args == NULL || _envCount == NULL || (env == NULL && *_envCount != 0))
 		return B_BAD_VALUE;
 
 	int32 envCount = *_envCount;

src/system/libroot/posix/unistd/exec.cpp

@@ -56,21 +56,24 @@ static int
 do_exec(const char *path, char * const args[], char * const environment[],
 	bool useDefaultInterpreter)
 {
-	int32 argCount = 0, envCount = 0;
+	if (path == NULL || args == NULL) {
-	char invoker[B_FILE_NAME_LENGTH];
-	char **newArgs = NULL;
-
-	if (path == NULL) {
 		__set_errno(B_BAD_VALUE);
 		return -1;
 	}
 
-	// count argument/environment list entries here, we don't want
+	// Count argument/environment list entries here, we don't want
 	// to do this in the kernel
-	while (args[argCount] != NULL)
+	int32 argCount = 0;
+	while (args[argCount] != NULL) {
 		argCount++;
-	while (environment[envCount] != NULL)
+	}
-		envCount++;
+
+	int32 envCount = 0;
+	if (environment != NULL) {
+		while (environment[envCount] != NULL) {
+			envCount++;
+		}
+	}
 
 	if (argCount == 0) {
 		// we need some more info on what to do...
@@ -78,7 +81,8 @@ do_exec(const char *path, char * const args[], char * const environment[],
 		return -1;
 	}
 
-	// test validity of executable + support for scripts
+	// Test validity of executable + support for scripts
+	char invoker[B_FILE_NAME_LENGTH];
 	status_t status = __test_executable(path, invoker);
 	if (status < B_OK) {
 		if (status == B_NOT_AN_EXECUTABLE && useDefaultInterpreter) {
@@ -90,6 +94,7 @@ do_exec(const char *path, char * const args[], char * const environment[],
 		}
 	}
 
+	char **newArgs = NULL;
 	if (invoker[0] != '\0') {
 		status = __parse_invoke_line(invoker, &newArgs, &args, &argCount, path);
 		if (status < B_OK) {