Fix crop_margin crash with extreme aspect ratio images (#17686)

Add bounds checking to crop_margin in GoTImgDecode, UniMERNetImgDecode,
and UniMERNetResize to handle edge cases:

- Return original image when cv2.findNonZero returns None (no text found)
- Return original image when bounding rect has zero width or height
- Return original image when cropped result would have aspect ratio > 200,
  which causes ValueError in downstream image processing

Fixes #17354

Co-authored-by: Lin Manhui <mhlin425@whu.edu.cn>

Author: Mr-Neutr0n

ppocr/data/imaug/unimernet_aug.py

@@ -495,7 +495,14 @@ def crop_margin(self, img):
         data = (data - min_val) / (max_val - min_val) * 255
         gray = 255 * (data < 200).astype(np.uint8)
         coords = cv2.findNonZero(gray)  # Find all non-zero points (text)
+        if coords is None:
+            return img
         a, b, w, h = cv2.boundingRect(coords)  # Find minimum spanning bounding box
+        if w == 0 or h == 0:
+            return img
+        # Avoid extreme aspect ratios that cause errors in downstream processing
+        if max(w, h) / min(w, h) > 200:
+            return img
         return img.crop((a, b, w + a, h + b))
 
     def get_dimensions(self, img):
@@ -595,7 +602,14 @@ def crop_margin(self, img):
         data = (data - min_val) / (max_val - min_val) * 255
         gray = 255 * (data < 200).astype(np.uint8)
         coords = cv2.findNonZero(gray)  # Find all non-zero points (text)
+        if coords is None:
+            return img
         a, b, w, h = cv2.boundingRect(coords)  # Find minimum spanning bounding box
+        if w == 0 or h == 0:
+            return img
+        # Avoid extreme aspect ratios that cause errors in downstream processing
+        if max(w, h) / min(w, h) > 200:
+            return img
         return img.crop((a, b, w + a, h + b))
 
     def get_dimensions(self, img):
@@ -720,7 +734,14 @@ def crop_margin(self, img):
         gray = 255 * (data < 200).astype(np.uint8)
 
         coords = cv2.findNonZero(gray)  # Find all non-zero points (text)
+        if coords is None:
+            return img
         a, b, w, h = cv2.boundingRect(coords)  # Find minimum spanning bounding box
+        if w == 0 or h == 0:
+            return img
+        # Avoid extreme aspect ratios that cause errors in downstream processing
+        if max(w, h) / min(w, h) > 200:
+            return img
         return img.crop((a, b, w + a, h + b))
 
     def get_dimensions(self, img):