Fix minor issues in user apps

Uninitialized variables, reading past array end, etc.

src/user/app/wc/wc.c

@@ -6,7 +6,7 @@
 #define BLOCK_SIZE 65536
 
 exit_code_t pass(uint64_t fd) {
-  static char buffer[BLOCK_SIZE];
+  char buffer[BLOCK_SIZE];
   uint64_t bytes;
   uint64_t total = 0;
   while ((bytes = read(fd, BLOCK_SIZE, buffer))) {