Fixed printf formatting for "%p" and added a unit test to check it

(cherry picked from commit c63aa9545eb800390176fd2fd86036da81f91100)

src/stdlib/SDL_string.c

@@ -1662,6 +1662,20 @@ static size_t SDL_PrintFloat(char *text, size_t maxlen, SDL_FormatInfo *info, do
     return length;
 }
 
+static size_t SDL_PrintPointer(char *text, size_t maxlen, SDL_FormatInfo *info, const void *value)
+{
+    char num[130];
+    size_t length;
+
+    if (!value) {
+        return SDL_PrintString(text, maxlen, info, NULL);
+    }
+
+    SDL_ulltoa((unsigned long long)(uintptr_t)value, num, 16);
+    length = SDL_PrintString(text, maxlen, info, "0x");
+    return length + SDL_PrintString(TEXT_AND_LEN_ARGS, info, num);
+}
+
 /* NOLINTNEXTLINE(readability-non-const-parameter) */
 int SDL_vsnprintf(SDL_OUT_Z_CAP(maxlen) char *text, size_t maxlen, const char *fmt, va_list ap)
 {
@@ -1794,6 +1808,9 @@ int SDL_vsnprintf(SDL_OUT_Z_CAP(maxlen) char *text, size_t maxlen, const char *f
                     done = SDL_TRUE;
                     break;
                 case 'p':
+                    info.force_case = SDL_CASE_LOWER;
+                    length += SDL_PrintPointer(TEXT_AND_LEN_ARGS, &info, va_arg(ap, void *));
+                    break;
                 case 'x':
                     info.force_case = SDL_CASE_LOWER;
                     SDL_FALLTHROUGH;

test/testautomation_stdlib.c

@@ -175,6 +175,12 @@ int stdlib_snprintf(void *arg)
     SDLTest_AssertCheck(SDL_strcmp(text, expected) == 0, "Check text, expected: '%s', got: '%s'", expected, text);
     SDLTest_AssertCheck(result == 7, "Check result value, expected: 7, got: %d", result);
 
+    result = SDL_snprintf(text, sizeof(text), "%p", (void *)0x1234abcd);
+    expected = "0x1234abcd";
+    SDLTest_AssertPass("Call to SDL_snprintf(text, sizeof(text), \"%%p\", 0x1234abcd)");
+    SDLTest_AssertCheck(SDL_strcmp(text, expected) == 0, "Check text, expected: '%s', got: '%s'", expected, text);
+    SDLTest_AssertCheck(result == SDL_strlen(expected), "Check result value, expected: %d, got: %d", (int)SDL_strlen(expected), result);
+
     return TEST_COMPLETED;
 }