fix: replace bare except with except Exception

Bare except clauses catch all exceptions including SystemExit and
KeyboardInterrupt. Replace with except Exception in image validation
functions (tfcv.py, pytorchcv.py) for ConvNets and TransferLearning.

lessons/4-ComputerVision/07-ConvNets/pytorchcv.py

@@ -134,7 +134,7 @@ def check_image(fn):
         im = Image.open(fn)
         im.verify()
         return True
-    except:
+    except Exception:
         return False
     
 def check_image_dir(path):

lessons/4-ComputerVision/07-ConvNets/tfcv.py

@@ -48,7 +48,7 @@ def check_image(fn):
         im = Image.open(fn)
         im.verify()
         return im.format=='JPEG'
-    except:
+    except Exception:
         return False
     
 def check_image_dir(path):

lessons/4-ComputerVision/08-TransferLearning/pytorchcv.py

@@ -134,7 +134,7 @@ def check_image(fn):
         im = Image.open(fn)
         im.verify()
         return True
-    except:
+    except Exception:
         return False
     
 def check_image_dir(path):

lessons/4-ComputerVision/08-TransferLearning/tfcv.py

@@ -48,7 +48,7 @@ def check_image(fn):
         im = Image.open(fn)
         im.verify()
         return im.format=='JPEG'
-    except:
+    except Exception:
         return False
     
 def check_image_dir(path):