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Fix use of zero-allocated memory

It's possible that the unsigned integer may overflow to zero,
and then we might use zero-allocated memory.

This is incredibly unlikely, and I would even go so far as to say
that this is a false positive. Fix it anyway, to silence this warning:

src/link/patch.c:92:24: warning: Use of zero-allocated memory
        stack.buf[stack.size] = value;
        ~~~~~~~~~~~~~~~~~~~~~ ^

Deal with overflow, and check for zero to get rid of the warning.

Signed-off-by: JL2210 <[email protected]>

--- a/src/link/patch.c

+++ b/src/link/patch.c

@@ -82,10 +82,18 @@

 static void pushRPN(int32_t value)

 {

 	if (stack.size >= stack.capacity) {

-		stack.capacity *= 2;

+		static const size_t increase_factor = 2;

+

+		if (stack.capacity > SIZE_MAX / increase_factor)

+			err(1, "Overflow in RPN stack resize");

+

+		stack.capacity *= increase_factor;

 		stack.buf =

 			realloc(stack.buf, sizeof(*stack.buf) * stack.capacity);

-		if (!stack.buf)

+		// || !stack.capacity to fix bogus

+		// zero-size allocation warning from

+		// scan-build, already caught above

+		if (!stack.buf || !stack.capacity)

 			err(1, "Failed to resize RPN stack");

 	}