Set stack size to minimum valid size if less requested

The stack size cannot be less than PTHREAD_STACK_MIN.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/platforms/posix/px4_layer/px4_posix_tasks.cpp

@@ -50,6 +50,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <pthread.h>
+#include <limits.h>
 
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -172,10 +173,13 @@ px4_task_t px4_task_spawn_cmd(const char *name, int scheduler, int priority, int
 		return (rv < 0) ? rv : -rv;
 	}
 
+	if (stack_size < PTHREAD_STACK_MIN) {
+		stack_size = PTHREAD_STACK_MIN;
+	}
 	rv = pthread_attr_setstacksize(&attr, stack_size);
 
 	if (rv != 0) {
-		PX4_ERR("pthread_attr_setstacksize returned error");
+		PX4_ERR("pthread_attr_setstacksize to %d returned error (%d)", stack_size, rv);
 		return (rv < 0) ? rv : -rv;
 	}