Fix minor issues in user apps

Uninitialized variables, reading past array end, etc.

src/user/app/cat/cat.c

@@ -5,7 +5,7 @@
 #define BLOCK_SIZE 65536
 
 exit_code_t pass(uint64_t fd) {
-  static char buffer[BLOCK_SIZE];
+  char buffer[BLOCK_SIZE];
   uint64_t bytes;
   while ((bytes = read(fd, BLOCK_SIZE, buffer))) {
     if (bytes == (uint64_t)-1) {

src/user/app/rm/rm.c

@@ -10,8 +10,7 @@ exit_code_t main(uint64_t argc, const char **argv) {
 
   uint64_t code = EXIT_CODE_OK;
   for (uint64_t i = 1; i < argc; i++) {
-    uint64_t removed = remove(argv[i]);
+    if (remove(argv[i]) == (uint64_t)-1) {
-    if (removed == (uint64_t)-1) {
       ERR_S("rm: could not remove file\n");
       code = EXIT_CODE_GENERAL_FAILURE;
     }

src/user/app/shell/shell.c

@@ -96,7 +96,12 @@ static void execute(char *command) {
   uint8_t pids_count = 0;
 
   for (uint8_t i = 0; i < subcommands_count; i++) {
-    string_trim(subcommands[i], ' ', &subcommands[i]);
+    if (!string_trim(subcommands[i], ' ', &subcommands[i])) {
+      if (subcommands_count > 1) {
+        ERR_S("Syntax error.\n");
+      }
+      break;
+    }
 
     char *argv[16];
     uint8_t argc = (uint8_t)string_split(subcommands[i], ' ', 16, argv);
@@ -166,7 +171,7 @@ exit_code_t main() {
   print_prompt();
 
   char line[256];
-  uint64_t offset;
+  uint64_t offset = 0;
 
   char chunk[64];
   uint64_t received;

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))) {