detect/mime: fix detect mime nits

Return 0 if .to_str() fails in functions
SCDetectMimeEmailGetData and SCDetectMimeEmailGetDataArray

Fixes:
431822c ("detect: add email.from")
96e461f ("detect: add email.received keyword")

rust/src/mime/detect.rs

@@ -27,8 +27,14 @@ pub unsafe extern "C" fn SCDetectMimeEmailGetData(
     ctx: &MimeStateSMTP, buffer: *mut *const u8, buffer_len: *mut u32,
     hname: *const std::os::raw::c_char,
 ) -> u8 {
+    *buffer = ptr::null();
+    *buffer_len = 0;
+
     let c_str = CStr::from_ptr(hname); //unsafe
-    let str = c_str.to_str().unwrap_or("");
+    let Ok(str) = c_str.to_str() else {
+        SCLogDebug!("Received non-UTF8 string in SCDetectMimeEmailGetData");
+        return 0;
+    };
 
     for h in &ctx.headers[..ctx.main_headers_nb] {
         if mime::slice_equals_lowercase(&h.name, str.as_bytes()) {
@@ -37,10 +43,6 @@ pub unsafe extern "C" fn SCDetectMimeEmailGetData(
             return 1;
         }
     }
-
-    *buffer = ptr::null();
-    *buffer_len = 0;
-
     return 0;
 }
 
@@ -69,8 +71,14 @@ pub unsafe extern "C" fn SCDetectMimeEmailGetDataArray(
     ctx: &MimeStateSMTP, buffer: *mut *const u8, buffer_len: *mut u32,
     hname: *const std::os::raw::c_char, idx: u32,
 ) -> u8 {
+    *buffer = ptr::null();
+    *buffer_len = 0;
+
     let c_str = CStr::from_ptr(hname); //unsafe
-    let str = c_str.to_str().unwrap_or("");
+    let Ok(str) = c_str.to_str() else {
+        SCLogDebug!("Received non-UTF8 string in SCDetectMimeEmailGetDataArray");
+        return 0;
+    };
 
     let mut i = 0;
     for h in &ctx.headers[..ctx.main_headers_nb] {
@@ -83,9 +91,5 @@ pub unsafe extern "C" fn SCDetectMimeEmailGetDataArray(
             i += 1;
         }
     }
-
-    *buffer = ptr::null();
-    *buffer_len = 0;
-
     return 0;
 }