fix(rla): immediate fix for PR #5153 error (#5172)

Caught in review, but I didn't see the comment before I merged.

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Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/rla.imageio/rlainput.cpp

@@ -509,9 +509,9 @@ RLAInput::decode_rle_span(span<unsigned char> buf, int n, int stride,
             ++e;
         } else {
             // run count negative: repeat bytes literally
-            if (count > n)
-                break;       // asking for a count that will overrun the buffer
             count = -count;  // make it positive
+            if (count > n)
+                break;  // asking for a count that will overrun the buffer
             for (; count && n > 0 && e < elen; --count, b += stride, --n)
                 buf[b] = encoded[e++];
         }