Fix segfault in filehandling due to incorrect use of signed vs unsigned int (#726)

This fixes bugs introduced in d905976

Author: PhracturedBlue

src/misc/fgets.c

@@ -19,7 +19,7 @@
 #if ! defined(EMULATOR) || EMULATOR == USE_INTERNAL_FS
 
 #define FILE void
-uintptr_t _open_r(void *r, const char *file, int flags, int mode);
+intptr_t _open_r(void *r, const char *file, int flags, int mode);
 int _close_r(void *r);
 int _read_r(void *r, char * ptr, int len);
 int _write_r(void *r, char * ptr, int len);
@@ -32,7 +32,7 @@ FILE *devo_fopen2(void *r, const char *path, const char *mode)
     int flags = (mode && *mode == 'w') ? O_CREAT : 0;
     int _mode = flags ? O_WRONLY : O_RDONLY;
 
-    uintptr_t fd = _open_r(r, path, flags, _mode);
+    intptr_t fd = _open_r(r, path, flags, _mode);
     if (fd <= 0)
         return NULL;
     return (FILE *)fd;

src/target/drivers/filesystems/syscalls.c

@@ -47,7 +47,7 @@ extern void init_err_handler();
 int FS_Mount();
 void FS_Unmount();
 
-uintptr_t _open_r(FIL *r, const char *file, int flags, int mode);
+intptr_t _open_r(FIL *r, const char *file, int flags, int mode);
 int _close_r(FIL *r);
 
 
@@ -127,7 +127,7 @@ void FS_CloseDir()
 {
 }
 
-uintptr_t _open_r(FIL *r, const char *file, int flags, int mode) {
+intptr_t _open_r(FIL *r, const char *file, int flags, int mode) {
     (void)flags;
     (void)mode;
 
@@ -204,7 +204,7 @@ int _write_r(FIL *r, char * ptr, int len)
 
 int _ltell_r(FIL *r)
 {
-    if ((uintptr_t)r > 2 && fs_is_open(r)) {
+    if ((intptr_t)r > 2 && fs_is_open(r)) {
         return (int)fs_ltell(r);
     }
     return -1;
@@ -214,7 +214,7 @@ int _lseek_r(FIL *r, int ptr, int dir)
 {
     (void)r;
 
-    if ((uintptr_t)r > 2 && fs_is_open(r)) {
+    if ((intptr_t)r > 2 && fs_is_open(r)) {
         if (dir == SEEK_CUR) {
             ptr += fs_ltell(r);
         } else if (dir == SEEK_END) {